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2009 Freelance Writing
Tanzanite Processing Steps at
Merelani Tanzania
FACE PICKING, ROM SORT RECOVERY, COBBING, CLARITY GRADING,
SIZING ONE, COLOUR GRADING, SIZING TWO AND CUTTING
Tanzanite the Uniqueness of Tanzania
Eng.Gilay Shamika2009
MINERALS AUDITOR IS
PRECISELY LIKE A
PILOT.
A SINGLE DISCREPANCY OF MINERALS WEIGHT WILL
CAUSE A HUGE TAX DEVIATION.
LIKEWISE
A SINGLE DISCREPANCY OF
A NEUTICAL MILE WILL CAUSE LANDING
DEVIATION
By Shamika, G.C
2009
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2009 Freelance Writing
1.0 INTRODUCTION
...............................................................................................................................
5
1.1 Mining
.........................................................................................................................................
5
1.2 Geology
.......................................................................................................................................
6
2.0 CLASSIFICATIONS OF TANZANITE GEMSTONES
...............................................................
7
3. 0 PROPERTIES OF TANZANITE
GEMSTONES.........................................................................
9
3.1 Unique features of Tanzanite
...................................................................................................
9
3.2 Optical and other Properties of Tanzanite
.........................................................................
10
3.2.1 Optical Properties
..............................................................................................................
10
3.2.2 Physical Properties of Interest
.......................................................................................
12
4.0 FOUR (4) CS OF GEMSTONES
.................................................................................................
13
4.1Source of Colour in Gemstones
..............................................................................................
14
4.2 Presence of Different Colors in a Gemstone
.....................................................................
15
4.3 Gemstones Colour Fade up
....................................................................................................
16
5.0 TANZANITE PROCESSING METHODS AT TANZANITEONE
........................................... 16
5.1 Concept 1
.....................................................................................................................................
16
5.2 Concept 2
.....................................................................................................................................
17
5.3 Concept 3
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18
6.0 DETAILED PROCESSING METHODS
.....................................................................................
20
6.1 Face picking
................................................................................................................................
20
6.2 ROM Sort recovery
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21
6.3 Cobbing
.........................................................................................................................................
23
6.4 Clarity
............................................................................................................................................
24
6.4.1 The meaning of An Inclusion
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26
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6.4.2Types of inclusions commonly found in Tanzanite gemstones
and other gems
............................................................................................................................................................
27
6.5 Grading the clarity of Tanzanite
...........................................................................................
27
6.6 Sizing Indicator
..........................................................................................................................
29
6.7 Sizing One (1)
..............................................................................................................................
30
6.8 Colour grading
............................................................................................................................
31
6.8.1 GIA Colour grading steps
................................................................................................
33
6.8.2 TanzaniteOne Colour grading
steps.............................................................................
34
6.9 Sizing two (2)
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35
7.0 GEMSTONE TREATMENTS, ENHANCEMENTS, AND CARE
.......................................... 36
8.0 GEMSTONES CUT AND POLISH
..............................................................................................
37
8.1 Cutting Techniques
...................................................................................................................
37
9.0APPENDICES
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38
Appendix 1: Birthstones & Anniversary Gemstones
.............................................................
38
Appendix 2: Anniversary Gemstones
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39
Appendix 3:
Weekday.......................................................................................................................
40
10: REFERENCES
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41
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Preface
It is not easy and will never be easy learning through
internet and practice. There is a need to stay in classroom
and learn about the gems for the benefit of my country.
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2009 Freelance Writing
1.0 INTRODUCTION
Tanzanite was formed over 600 million years ago when Mt.
Kilimanjaro erupted caused a unique set of conditions to form deep
within the earth - heat and pressure mixed with rare chemicals such
as Vanadium to allow this exceptionally rare gem stone to form.
These conditions remained constant for the entire 600 million years
and Tanzanite grew. It was first discovered by man in 1967 when an
enormous grassfire swept the land below Kilimanjaro Mountain. As
Tanzanite is a brownish color in its rough state, the crystals
lying on the surface were never noticed until when the grassfire
had burnt the land and heated the stones. They turned bright,
glittering violet-blue in the sunlight and attracted the attention
of some Maasai tribesmen.
Tanzanite was named by Tiffany & Company (New York) and for
the first ten years after its discovery Tiffany's had the exclusive
right to this lovely gem stone. Today, after the liberalization of
the Tanzanian economy, it is a free market.
To date the only known reserve of Tanzanite gemstone in the
world is a strip of
8km by 1km at Merelani area in Manyara region, Northern of
Tanzania. Tanzanite is
believed to be discovered at the area in 1967 and in 1971, the
tanzanite mines were
nationalised and mining was taken over by the State Mining
Corporation, STAMICO.
Production records for the first five years indicate a decrease
in grades, mainly
attributed to haphazard mining and theft. During 1978, Tanzania
Gemstone
Industries, a state organisation established by STAMICO,
published a report
recommending the viability of full scale mining of gemstones. No
meaningful action
was taken. During the next ten years, production decreased.
There was also an
increase in informal, artisanal mining. By 1989, an estimated
30,000 artisanal miners
were working in the area.
In 1990, the Tanzanian Government curbed artisanal mining and
demarcated
the area into Blocks A, B, C and D. Block A was awarded to
Kilimanjaro Mines
Limited, Blocks B and D to small-scale miners and Block C to
Graphtan Limited, a
graphite mining company. Graphtan ceased mining activities in
1996 and Afgem
acquired the mining licence for Block C. In 2000, Afgem
completed a feasibility study
for the commercial mining of tanzanite and mine development
commenced in 2001. In
2004, the TanzaniteOne Group acquired Afgem's tanzanite business
and assets.
1.1 Mining
The mining method employed at TanzaniteOne mining Ltd is
Underground
Mining. Currently there are six operational shafts in their SML
which stretch by 1km
by 2km. These operational shafts are ; Bravo shaft, CT shaft,
Main shaft, Askari shaft,
Delta shaft and Investor shaft which is used as hoisting shaft
for Main shaft, Delta
shaft, and Askari shaft to bring out ores. Two shafts TC and JW
are not operational.
Mining currently takes place through five shafts: Delta, Askari,
Main, CT and Bravo
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2009 Freelance Writing
shafts. Shafts are sunk at an angle of 42 along dip of the JWZ
mineralisation zone.
The shafts are fitted with tracks and material is removed via a
hoist and inclined shaft
structure. Drives are driven along strike at an angle of 16
along the plunge of the
fold noses. A monorope (endless looped rope and pulley) system
is used to remove
materials in bags from the mining fronts towards the inclined
shaft ore pass
infrastructure. Blasting is used as the main method of mine
advancement. Once
favourable boudin structures are approached pneumatic drilling
and handpicking is
used to remove tanzanite as carefully as possible.
1.2 Geology
Tanzanite is a thousand times rarer than diamonds and is
trichroic, which
means that in its rough form, it radiates three different
colours from each of its
crystallographic axes: blue, violet and burgundy. Tanzanites are
found in Lelatema
Antiform in Merelani, Manyara Region, Northern Tanzania. It is
believed to be formed
600 million years ago.
3Tsavorite + H2O + 5CO2 = 2Tanzanite + 3Quartz + 5Calcite
Tanzanite is found within a relatively complex geological
environment and is found in
'chocolate-tablet' boudin structure, typically located in the
hinges of isoclinal folds
(folds dipping in the same direction) present in the ore body.
The Geologists at
Tanzanite one has identified two potential strips of these
unique zones in the area and
has named them as Upper Horizon and Lower Horizon. The familiar
and currently
mined is the JW zone in Lower horizon, named after Ally Juyawatu
who is believed to
be the first miner in the area. Deep hole drilling, geophysics,
geochemical analyses
and structural and geological mapping have all increased the
level of geological
knowledge. Drilling programme has shown that the lower horizon,
which hosts the
economic mineralisation, extends three times further dip than
initially anticipated.
This databank of proprietary geological know-how is unrivalled
and will become more
important than ever as mining operations deepen and the
artisanal mining styles
employed on the other license blocks become redundant.
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2009 Freelance Writing
2.0 CLASSIFICATIONS OF TANZANITE GEMSTONES
The gemstones are classified according to the clarity (the
extent of inclusion free) and
colour. There are standards used to explain the inclusion
effects on the gems quality
set by GIA. For Tanzanite gemstones, the TanzaniteOne Mining
Company has its own
standards special for Tanzanite. Let us start by looking on them
before we go into
classifications. Just the abbreviations and what they mean but
you will broadly have
full dose of Inclusions on the section of Clarity grading.
(Table 1, 2 &3)
Table 1: GIA Standards
Inclusion Abbreviation Explanation/What is seen in Gems
VVS Very Very Slight
VS Very Slight
SI1 Slight Included 1
SI2 Slight Included 2
I1 Included 1
I2 Included 2
I3 Included 3
Table 2: TanzaniteOne Standards
Colour and Inclusion Abbreviation
Explanation/What is seen in Gems
A Exceptional Colour, Eye Clean
B Rare Deep Blue/other Colour, Eye Clean
BSI B Colour-Slightly Included
BI B Colour Included
BL B Lighter Colour Grade, Eye Clean
BLSI B Light-Slightly Included
BLI B Light Included
D Opaque Material(agreed to use D instead of O )
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Table 3: The effect of Inclusions on the types of Gemstones
Type of Gemstones Inclusions Effect
Type 1 Gemstones
VVS minute to not detectable
VS minor
SI1 NOTICEABLE to obvious
SI2 OBVIOUS to noticeable
I1 prominent to moderate effect on appearance or durability
I2 prominent to severe effect on appearance or durability
I3 prominent to severe effect on beauty, transparency, or
durability
Type 2 Gemstones
VVS minor
VS NOTICEABLE to obvious
SI1 noticeable to OBVIOUS
SI2 obvious to prominent
I1 prominent - moderate effect on appearance or durability
I2 prominent - severe effect on appearance or durability
I3 prominent - severe effect on beauty, transparency, or
durability
Type 3 Gemstones
VVS NOTICEABLE to obvious
VS noticeable to OBVIOUS
SI1 obvious to prominent
SI2 obvious to PROMINENT
I1 prominent to considerable effect on appearance or
durability
I2 prominent to severe effect on transparency or durability
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I3 prominent to severe effect on beauty, transparency, or
durability.
3. 0 PROPERTIES OF TANZANITE GEMSTONES
Tanzanite is an exceptionally rare gem stone- estimated at a
thousand times rarer than diamond. There is only one source for it
in the world - on the slopes of the
legendary Mt. Kilimanjaro at Merelani Tanzania.
3.1 Unique features of Tanzanite
Tanzanite is among the few gem stones in the world that are
"trichroic". This means that when white light passes through, it
breaks into 2 paths and creates 3 different colors - one axis will
look violet, reddish brown and the third a blue-violet. The picture
below shows the same Tanzanite crystal from 3 different angles
showing its
amazing trichroism.
Figure 1: Three colours of Tanzanite in response to light
In the rough state most Tanzanite is predominantly brown and
blue. Heating at 600 degrees centigrade causes this color to change
to blue violet. This is a permanent and stable change. Tanzanite
due to its trichroism characteristic has never been
synthesized, but a number of imitations exist and the most
common is blue-violet glass. A synthetic fosterite has also been
used as an imitation and is known as Tanzanique in the trade. It
does not have the same trichroism so is easily distinguished from
the real Tanzanite.
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Table 4: Gemological Properties of Tanzanite Gemstones
Gemological Properties Unit of Measure
Gem Species Zoisite
Specific gravity 3.35
Hardness (Mohs Scale) 6.5
Toughness Fair
Stability to light Stable
Carat Weight Below 1-10 ,rarely 100
+
Birthstone December
A great deal of Tanzanite marketing makes a big deal of the "red
flash" phenomenon of Tanzanite. This is one of the features of the
stone and is due to Tanzanite's trichroism. Tanzanite is extremely
light sensitive, with incandescent lighting (yellow lighting found
in common light bulbs) tending to shift its color to the violet
side causing the red and pink flashes to appear within the stone.
The images below of the same stone show it under white (daylight)
and under incandescent light:
Under white light
Under incandescent light
3.2 Optical and other Properties of Tanzanite
This is very important to be pinpointed particularly by Clarity
and Colour graders of
the Tanzanite. Is through these properties one can master the
colour and clarity
grading. Knowing how the light breaks down into spectral colours
through the
Tanzanite gem will help the colour and clarity grader where to
focus (the position of
eyes) during grading. Therefore kin observations of these
optical properties will pave a
way for real gems valuation rather than being on the eyes of
beholder.
3.2.1 Optical Properties
The optical properties are the major properties of gemstones
which distinguish them
from precious metals/minerals which are completely opaque in
response to light.
The figures below (Figure 2 & 3) show the optical properties
of Gemstones in response
to white light when passes through;
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2009 Freelance Writing
Dispersion: This is the splitting of light as it enters a
gemstone. Colors separate
during refraction of white light, which leads to seeing fire in
a gem. By this
property, the internal features of the gem can be identified and
hence used as a
distinguishing feature from other gems classification. The
dispersion index
differs from gem to gem due to anatomy of each type of gem and
inclusions
found within a gem type.
Refraction: The bending of light (or any wave phenomenon) when
it moves
between media with different conductive velocities. Refractive
Index is the ratio
of the velocity of light in a vacuum to that in the substance;
it determines the
angle at which light bends when it enters a substance
obliquely.
Double Refraction: A phenomenon which occurs when the ray of
light entering
a crystal is refracted and divided into two rays instead of one.
This is most
commonly seen in Calcite and Zircon.
Luster: The manner in which a mineral/gemstone reflects light
from its
surface; it is affected by the surfaces smoothness and
reflectivity. Rough and
polished tanzanite will respond slightly different;
Figure 2: Dispersion of the original white light through a
prism.
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Figure 3: Dispersion of the original white light through a
gemstone.
Points to ponder from above:
In a gem the dispersion occur parallel to the source of light
with different direction to each other and;
Dispersion occurs in the same side of source of light.
Note: These optical findings are very important properties to
identify where to watch the colors of the gem relative to the
source of light; they provide the location of eye and
identification of number of colours in a gem.
3.2.2 Physical Properties of Interest
Gems are subjected to treatments and enhancements for quality
improvement.
Heating, Cutting and polishing are the methods used for quality
improvements. These
can only be done after studying the physical properties of the
gem concern otherwise
the treatments and enhancements cant be achieved.
Cleavage: The tendency of a mineral /gemstone to break along a
plane due to a
direction of weakness in the crystal. Minerals and gemstones can
be split along
certain flat planes which are called cleavage. Cleavage is
related to the lattice
(the cohesive property of the atoms) of the crystal.
Fracture: A break with an uneven or irregular surface crack.
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Tenacity: The strength of a mineral/gemstone. It is also its
resistance to breaking, crushing, bending, crumbling, tearing, or
changing shape. There are several different terms used to denote a
minerals tenacity. They are listed below.
-Elastic: It can be bent and will resume its previous shape when
let go.
-Ductile: It can be pulled and made into very thin threads.
-Flexible: It can easily be bent without breaking and can be
shaped.
-Fragile: It will easily break into pieces.
-Friable: It crumbles easily.
-Malleable: It can be flattened out into thin sheets without
breaking.
-Sectile: It can be cut into shavings with a blade.
The above optical and physical properties are extremely
important for all concerned
with gemstones to know the different values and measurements of
gemstones. Without
knowing these values, it would be extremely difficult for anyone
to be able to identify
one gemstone from another.
4.0 FOUR (4) CS OF GEMSTONES
The Colour, Clarity, Carat weight and Cut are termed as 4cs of
the gemstones. These
are the factors used for grading the quality and price of the
gemstones.
Color is the main indicator of value of Tanzanite, the more
vivid pure and
bright a color is, the more it is valued. Tanzanite exists in
three different
colours when subjected into natural light or fiber light. But
with a single glance,
it appears predominantly brown and Blue-violet into light.
However when it
comes into colour grading, colour remains a subjective "eyes of
the beholder"
sensation. The most colorful Tanzanite is graded as AAA grade
for GIA
Standards and A grade for TanzaniteOne Standard.
Clarity is a major factor in determining quality and,
consequently, the value of
a gem. This refers to what extent the gemstone is flawless or
clear without
inclusions. The more the gemstone is clear (without inclusions)
the more the
value of the gemstone. Inclusions not only distract the eye, but
interfere with
the behavior of light in the gem, and have a significant effect
on brilliancy.
However; inclusions that do not affect the durability of colored
are not an issue
in determining value as corresponding inclusions in
diamonds.
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2009 Freelance Writing
Carat weight is the international standard unit for gemstones.
All gemstones
price is based on carat weight. One carat (1Ct) equals to
0.2g.Tanzanite is
almost found in the range of 1-10 carats but rarely up to
20-100+ carats.
Cut has the least impact on a value of the gems among other 4
C's although
due to competition with other gems with posh cuts, the cut of
Tanzanite is
important to add value. Cut shapes and cutting techniques will
be discussed in
the Cutting section.
4.1Source of Colour in Gemstones
Color results from a minerals chemical composition, impurities
that may be present, and flaws or damage in the internal structure.
Most minerals are usually white or colorless in a pure state. Many
impurities can color these minerals and make their color variable.
Some crystals get their color from growth imperfections. Growth
imperfections interfere with light passing through the crystal
making it appear darker or nearly black.
Idiochromatic minerals are "self colored" due to their
composition. The color is a constant and predictable component of
the mineral.
Allochromatic minerals are "other colored" due to trace
impurities in their composition or defects in their structure. In
this case, the color is a variable and unpredictable property of
the mineral.
Pseudochromatic minerals are "false colored" due to tricks in
light diffraction. The color is variable but a unique property of
the mineral, such as the colors produced in precious opal and the
shiller reflections in Sunstone and Labradorite.
The most common trace elements/coloring elements in minerals
are: Beryllium, Chromium, Cobalt, Copper, Iron, Lithium, Manganese,
Nickel, Sulfur, Titanium,
Uranium, and Vanadium.
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4.2 Presence of Different Colors in a Gemstone
Color is the most important characteristic of tanzanite
gemstones. For the Diamonds it is the absence of color which is
most important.
Light absorption and Trace elements are most factors for having
different colours of gemstones;
Color is produced by the way a gemstone absorbs light. Light is
an electromagnetic vibration at certain wavelengths, but the human
eye can
only perceive certain wavelengths. There are several different
reasons why
the various gemstone varieties absorb light differently. Some
gemstones are said to be idiochromatic or self-colored. They absorb
certain wavelengths of light due to characteristics of their
chemical structure. Most gemstones are allochromatic. They are
colored by impurities or trace elements in their crystal
structure.
The relationship between a chemical impurity and a gemstone
color is not a simple one. Sometimes a similar color can result
from different trace elements. Also, a single trace element can
produce different colors in different gem varieties. This is
because there is a complex relationship between the gem's crystal
structure and the trace elements.
Another way in which gemstones acquire color is through human
intervention in the form of gem treatments. Heat treatment is often
used to change the chemical state of
an impurity to deepen or lighten color, reduce a certain hue, or
improve clarity. Gemstones are also dyed, treated with chemicals,
coated with chemicals or metals, irradiated, and artificially
colored in many other ways to alter their appearance. All gemstone
treatments must be disclosed by the vendor prior to the sale of the
gemstone.
Through my experience as a Senior Minerals
Auditor (TMAA) at TanzaniteOne I have
observed the following by using fiber light;
If all the different wavelengths of light pass
through a gemstone, it appears colorless.
On the other hand, if the gem material
absorbs all the light, it attains maximum
intensity of its colour (extremely deep/Black)
and;
If a stone absorbs all wavelengths except
those in the red part of the spectrum, the gem
appears red.
The literature also supports these
observations. The effect depends on the
intensity of light applied (Incandescent lights
6200K onward)
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2009 Freelance Writing
4.3 Gemstones Colour Fade up
The colors of some minerals and gemstones can be altered by time
or exposure to sunlight or bright display lights. Some may fade,
while others may oxidize. Some porous gems, such as Agate, Lapis
Lazuli, Pearls, and Turquoise may be treated to stabilize their
color. Gemstones that have had their color altered through the
various treatments may also fade, change color, or become spotty
over time.For tanzanite is not the case. The colour attained by
heat treatment that is Blue Violet is a permanent change. Even the
brown colour which is predominant at its ground state does not fade
at all. It only changes when subjected into heat to blue
violet.
5.0 TANZANITE PROCESSING METHODS AT TANZANITEONE
The discussions will be based on the methods used for Tanzanite
gemstones processed
at TanzaniteOne. The prime methods are underway in the Sort
house and other
methods that are cutting and polishing carried in Cutting house.
The discussion and
explanations will base on experience grabbed in Sort house.
Probably next compilation
will include everything done in cutting house-Cut, pre-formed
and polishing. But in
this compilation, cutting methods and shapes will only grossly
highlighted.
Before going into processing methods, it is healthiest to
renaissance three concepts to
bring in perfect understanding when discussing those methods
practiced at
TanzaniteOne. I have conceptualized a figurative imagination to
enhance
understanding of the gemstone processing methods.
(Therefore the Concepts below are subjective to Compiler and not
referred from
anywhere)
5.1 Concept 1
TanzaniteOne not only produce Tanzanite but also Tsavorite and
other Coloured
gemstones. Therefore bear in mind, you will find other gems and
not Tanzanite only
and;The Colour referred is Blue even for those which are not
blue are named after it.
The table below justifies the said.
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2009 Freelance Writing
Table5: Colour coding at TanzaniteOne
COLOUR EXPLANATION
A Exceptional Colour, Eye Clean
B Rare Deep Blue/other Colour, Eye Clean
BSI B Colour-Slightly Included
BI B Colour Included
BL B Lighter Colour Grade, Eye Clean
BLSI B Light-Slightly Included
BLI B Light Included
D Opaque Material(agreed to use D instead of O )
5.2 Concept 2
Try to imagine gemstone is like a Pineapple in which the first
step is to pick it (face
picking) from the market wash it (Sort) start peeling (cobbing),
Cut it (sizing one) up to
the last stage of the pineapple peeling and cutting which you
remain with inner rod
like feature protruding at the bottom where you hold (Sizing
two).OR Imagine the
Pancake being cut symmetrical inwards until you leave the last
portion at the middle.
Assimilate above scenarios with the Tanzanite processing
methods-The gemstones are
brought (face picking) from the mining site/shaft to the Sort
house for processing.
Each step reduces the gemstones (like pineapple example) up to
the last step (sizing
two) where you get minimal Sizes. Observe the diagram below for
support;
Face picking being the first method where you have large
gemstone (the whole
pineapple) and the last stage is Sizing two (nice pieces of
pineapple with different sizes
ready to eat)
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2009 Freelance Writing
Figure7: Concept on Size reduction related to Gemstones
processing steps.
5.3 Concept 3
From the above concepts, carry on thinking the example of
pineapple. From pineapple
you will have materials (peels and rod like at the middle) to be
discarded and those for
eating. But due to massive demands of materials for production
in different sectors,
these days nothing is discarded.
The same happen in gemstone processing methods. Along the
processing methods,
there are materials of irrelevant but are then sold locally. The
processing methods are
summarized below in Table 6 with the explanation of what is left
and what is
seconded in the next or iteration stages.
1. Face Picking
2. ROM sort rrecovery
3. Cobbing
4. Clarity grading
5. Sizing One
6. Colour grading
7. Sizing Two
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2009 Freelance Writing
Table 6: The Gemstone processing material balance
PROCESS/METHODS CARRYOVERS /LEFTOVERS
Face Picking
The gems are picked from the shaft just by looking on the face
of it and
identify it. They are normally large stones. Those which are
clean go to cutting
section and those which are attached or embedded to normal
stones; they
have to be brought in the sort house for sort recovery and the
rest of the
methods.
Romsort Recovery The process of sorting materials from the
run-of-mine and discord unwanted
materials. The recovery gems are then seconded to cobbing.
Cobbing
Gems from ROM Sort recovery are cobbed and graded into A-C, D
grade,
Colour, Tsavorite, Waste and Off-Cuts.
Carry Over: A-C carried to Clarity grading while Coloured
(greenish gems) are
taken to Cutting process or sold as they are.
Left Over: D grade, Coloured, Tsavorite, Waste and Off-cuts are
collected for
local selling and sometime for export.
Clarity Grading
A-C gems from cobbing are clarified into A, B, BL and SI, I.
Carry Over: A, B and BL gems are carried to colour grading
without passing
into sizing 1. While SI and I gems are carried out into Sizing
1
Left Over: Nothing left here, all materials are in transit
Sizing One
SI and I gems from Clarity section are sized into ranges from
size 1 to 14. At
sizing 1, the gems with the weight from 0.01 up to 0.49grams are
arranged
here and those above, from 0.5 up to 20+grams are taken to
Sizing 2 for more
weight arrangements.
Carry Over: SI and I Gems with size 5 to size 14 are carried to
Colour grading
while;
Left Over: SI and I Gems with size 1 to size 4 are collected
ready for selling.
Colour Grading
At this section remember we have A, B and BL gems from Clarity
section and
also SI and I Gems with size 5 to size 14 from sizing 1 section
carried to Colour
grading. Therefore these are our feed to be processed. The
common useful
methods used for colour grading is from GIA (Gemology Institute
of America).
Carry Over: The colour of A, B and BL gems are enthusiastically
confirmed
while SI and I Gems are classified into relation to A,B and BL
to get their
hybrid i.e. A(I),A(SI),AL(I) and AL(SI) but these have never
been obtained.
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2009 Freelance Writing
Therefore only BI, BSI, BLI and BLSI are graded from SI and I.
That means
broadly there will be A, B, BL, BSI, BI, BLSI and BLI. But
grossly colour
grading can end at A, B, BL and C. That means all gems with
inclusion are
generalized as C (BSI, BI, BLSI and BLI)
Left Over: No materials are left here. All colour graded gems
are carried to
Sizing two.
Sizing two
The intention of this section is to grade the gems according to
their weight
starting from Size 5. We already have colour grading; the last
stage is to
arrange those gems with reference to their weight and colour.
The gems with
the same size and colour are mixed together and weighed.
This is the last stage where the gemstones after being sized
according to colour
and weight, they are packed ready for selling.
The detailed explanations will include the vivid example of what
is done in all
methods at TanzaniteOne Mining Company.
6.0 DETAILED PROCESSING METHODS
The whole seven (7) processing methods undertaken at
TanzaniteOne will be discussed
with detailed example for each method.
6.1 Face picking
The gems are picked from the shaft just by looking on the face
of it and identify it.
They are normally large stones, medium and small. They comprise
wanted and
unwanted materials. All materials are brought in the Sort house
for clean up and
weighing. Those which have no inclusion, the decision need to be
made whether to sell
as they are or go to cutting and those which are attached or
embedded to normal
stones and inclusions, they have to remain in the sort house for
sort recovery and
other processes. These are like alluvial gold (course particles
of gold) picked from Ores
or collected on gravity circuit (free/liberated gold).Table 7
shows the practical example
of face picking;
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2009 Freelance Writing
Table 7: Practical example for Face picking
Total weight Picked from Pit (g)
Total weight of grade D (g) Total weight for cobbing (g)
Shaft
10383.99 4616.04 4567.95 MAIN
Source: TMAA
Explanation based on the above practical example
Total weight Picked from Pit: This is the total weight of
materials picked from
the pit. They are picked by the miners just by looking and find
them as the
gemstones and packed into bags, all the way to Sort house.
Total weight of grade D: The materials from the pit are then
checked for
confirmation. They have to be washed to see them clearly. Those
which are
Opaque are the ones called grade D and the other which are
transparent and
pass the light by showing their true colour, are the real
gemstones separated for
cobbing. Hence total weight of D grade means the weight of
Opaque materials.
They are gemstones with less value. They dont exhibit the true
properties of
tanzanite.
Total weight for cobbing: This is the weight of real gemstones
to be taken to
the next process of cobbing. The real gemstones are cobbed to
remove
unwanted materials attached to them. But also reduces the
gemstones into
reasonable sizes to ease clarity and colour grading.
Shaft: This is the area where those materials have been picked/
mined. It is
called shaft because the place is underground where you need to
descend by
shaft. Therefore the mining area is named after it. In this
example the
gemstones were brought from Main Shaft.
6.2 ROM Sort recovery
This is the process of sorting/separating materials from the
run-of-mine (ROM).It is
the same as face picking logically but the difference is;
ROM is the pile of materials (ores) with general geological
estimation of grade
e.g. 5g/t. That means for every tone there is 5gram of
required
gemstone/minerals.
The second difference from face picking materials is that, the
materials from
ROM need to be crushed to the required size before brought in
the Sort house
for sorting i.e. separation of gemstones, D grade and other Taka
Taka.
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2009 Freelance Writing
The Crushed materials from ROM are stored into bags and drums.
Sorting is
done by taking substantial portion of materials depending on the
number of
Sorters.
To avoid direct contact of materials for security purposes, the
sorting and all
other methods are done in the housing cabins.
Table 8: Practical example for ROM Sort recovery
Total weight from ROM( g) Total weight recovery (g)
147100 gm 10764.20gm
Explanation based on the above practical example.
Total weight from ROM: This is the weight of portion of ROM
materials given
to sorters on a particular day for sorting required and unwanted
materials.
Total weight recovery: This is the weight of required materials
(recovery)
obtained from ROM materials.
Therefore ROM sort recovery is the process of separating
gemstones and other
materials from the process plant crusher brought by conveyor.
The separation/sorting
is done manually. For gold the crushed materials from the mill
go into cyanidation and
leaching BUT for gemstones the crushed materials are then sorted
by hand to get the
gemstones. (Figure)
Figure 8: ROM Sort recovery process. The spatula-like equipment
is used for sorting
rather than fingers for security purpose.
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2009 Freelance Writing
6.3 Cobbing
Is the trimming of gemstones to remove unwanted materials and to
reduce the gems
into reasonable sizes for easiest of undertaking clarity and
colour grading.
The small whippy hammers are utilized delicately to remove
unsatisfactory materials.
Despite the loss of weight necessarily incurred in the cobbling
process (off cuts), the
remaining material is upgraded to such an extent that it brings
a price more than the
original gems and makes up for the weight loss and cost of
labor. Let us remind
ourselves about the following which had already previously
discussed;
Remember from face picking and ROM sort recovery, required
materials were taken to
this stage. In previous pages we have mentioned that at
TanzaniteOne not only
tanzanite is available but also other gemstones. The practical
example below depicts
the gemstones available-Coloured gemstones, Tsavorite gemstones
which is also
available at Kenya Tsavo national park and is named after
it.
Table 9: Practical Example for Cobbing
Total weight(g) A-C D grade Coloured Tsavorite Waste Off-cut
Total weight(g)
10701.5 1805.35 5160.94 334.78 53.89 334.39 3009.53 10698.88
Explanation based on the above practical example
A-C: TanzaniteOne during Cobbing they combine all gemstones with
inclusions
and name them as C grade. Therefore whenever you see Colour
grade C it
means the whole package of BSI, BI, BLSI and BLI.
Therefore in practice A-C means combination of all colours A, B,
BL, BSI, BLSI,
BI and BLI (revise colour grading standards at TanzaniteOne
pg)
Coloured: These are the gemstones available at TanzaniteOne
which do not
have the real colour of tanzanite.
Tsavorite: Tsavorite gemstones are also available at Kenya Tsavo
national park
and are named after.
Off-cut: These are small pieces of all gemstones available
during
hammering/cobbing of gemstones. They are used for mixing with
other
materials to make Tiles and other ceramic items for shining the
surface.
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2009 Freelance Writing
Figure 9: The cobbing process at TanzaniteOne.
6.4 Clarity
Clarity is the second most important of the 4c's when
considering Tanzanite quality.
Clarity simply refers to how inclusion-free a gemstone is. Once
again, the most
universally accepted and most documented system is the GIA
system but there are
also numerous other trade based systems in use like the one used
at TanzaniteOne as
seen in previous chapters. The other system commonly used is
Munsel System but
will not be discussed, have a time to web it.
The discussion will only base on GIA system and its TanzaniteOne
derivative system
for tanzanite. Below is a chart showing the GIA and TanzaniteOne
clarity/colour
grading system which will be referred in our discussions. The
TanzaniteOne
Standards is the one which is emphasized since we are deeply
dealing with
tanzanite in our compilation.GIA system is revised for building
the concept related
to TanzaniteOne Clarity/Colour grading standards. Figure. And
Table 10 indicates
the level of inclusions and how those levels can be graded.
A B/BL BSI BLSI BI- BLI (TzOne System)
Figure 10: GIA and TanzaniteOne Clarity grading
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2009 Freelance Writing
Explanations of level of Inclusions
VVS: This is the top grade in the GIA system. Tanzanite is
classed by the GIA as
a "Type 1" gem which means it is graded very strictly. Stands
for Very very
slightly included and whilst most VVS Tanzanites are flawless
they can contain
minute inclusions which are difficult to see with a loupe (10x
magnification)
and invisible to the unaided eye. Typical minute inclusions may
be very fine
needles, tiny hairline feathers, very faint clouds and
percussion marks.
VS: This stands for Very Slightly Included and these stones are
characterised
by minor inclusions which are somewhat easy to see under 10x
magnification
but usually invisible to the unaided eye. Typical inclusions may
be small
included crystals, liquid inclusions, fine needles, small
feathers
SI1 - SI2: This stands for Slightly Included and these stones
are characterised
by noticeable inclusions which are apparent under 10 x
magnifications. In SI1
they are usually visible and SI2 quite visible to the unaided
eye. Typical
inclusions are included crystals, large liquid inclusions,
feathers, dense clouds.
I1-I2-I3: The lowest grade. Stands for Imperfect. These stones
are characterised
by inclusions that have a negative effect on either appearance,
durability or
both. At I1 there is a moderate effect on either factor, I2 a
severe effect on both
factor and I3 a severe effect on both factors.
Table 10: The summarized level of inclusions
GRADE STANDARD WHAT YOU SEE
VVS
Very, Very Slightly included -
Inclusions are easily seen
under 10X magnification, but
usually not visible to the
unaided eye.
The gem is almost perfectly
transparent. If you examine
the stone closely enough, you
may see very tiny flaws.
VS
Very Slightly included -
Obvious inclusions are easily
seen under 10 x
magnifications, and usually
visible to the unaided eye.
The gem is still transparent
and lively. On close
examination, a few small
flaws can be seen.
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2009 Freelance Writing
SI 1
Slightly Included 1 -
Inclusions are large and
numerous under 10x
magnification, and prominent
to the unaided eye.
The gem is mostly
transparent, but one or more
flaws are easily visible.
SI 2
Slightly Included 2 -
Inclusions are large and
numerous under 10x
magnification, and very
prominent to the unaided eye.
The gem is generally
transparent, but has a
number of large flaws.
I 1
Included 1 - Inclusions are
very obvious and have a
moderate negative effect on
the appearance OR durability
of the stone.
The stone either has so many
inclusions that it is only
partly transparent, or if
transparent it has one or
more cracks that might
weaken the gem.
I 2
Included 2 - Inclusions are
very obvious and have a
severe negative effect on the
appearance OR durability of
the stone.
The stone either has so many
inclusions that it appears to
be translucent, or if
transparent it has cracks that
could weaken the gem.
I 3
Included 3 - Inclusions are
very obvious and have a
severe negative effect on
BOTH the appearance AND
durability of the stone.
The stone has so many
inclusions that it appears to
be translucent, AND it has
one or more cracks that
weaken the gem
6.4.1 The meaning of An Inclusion
The inclusions are virtually materials other than original
gemstones. They may be formed before, after or on the same time
with the gemstones. Broadly is defined as; Any irregularity or
dislocations in a crystal's lattice, or structure, marks of the
crystallization phases, color striations, and internal fractures,
which may be caused by internal stress or external pressure.
Simply the material trapped within the body of a crystal which
is different from the primary elements of the host crystal.
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2009 Freelance Writing
6.4.2Types of inclusions commonly found in Tanzanite gemstones
and other gems
Crystals feathers, needle like, cracks, healed fractures and
included lily pads and foils.
Individual pinpoints, included crystals, voids Clusters of
included crystals, or voids Clouds of pinpoints
There are three types of inclusions, or processes, through which
other materials can get into a crystal;
Protogenetic Inclusions: These inclusions were already present
before the host mineral was formed. The host mineral grew around
them. Therefore they are older than the host crystal.
Syngenetic Inclusions: Formed at the same time as the host
mineral. These inclusions can be solids, liquids, or gases, or
combinations of any of the three forms of matter. These inclusions
are therefore the same age as the host crystal.
Epigenetic Inclusions: These inclusions were formed after the
host crystal was formed. These inclusions are usually either formed
by exsolution or from the recrystallization of a fracture in a host
mineral. They may also be liquid, solid, or gaseous. These
inclusions are therefore younger than the host crystal.
6.5 Grading the clarity of Tanzanite
Most color stone clarity grading is assumed to be with the
unaided eye. The Sunlight
is used to see the clarity through/within the gemstone. But the
specialized dealers
and companies of gemstones use the special equipments to
minimize the human error
especially if your eyesight is below standard. The fiber light
is used at TanzaniteOne
and magnification lens (10 x magnifications).
Carefully study a gemstone, observing characteristics that
distract the eye or
could affect durability, transparency, brilliance and color.
Mentally summarize
those observations and ask yourself in which category the gem
belongs. If you
notice a minor inclusion, start your grading assessment again
with that clarity
grade as a minimum.
The logic behind is to grade A/B/BL and SI/I from the cobbed
Tanzanite.
A/B/BL are combined while SI/I are separated.
At this process weight is not considered, only inclusion
matters. Bear in mind
here B do not only signify blue but also other colour rather
than Blue. The same
rules as of Blue colour apply to other colour and named after
A/B/BL and SI/I.
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2009 Freelance Writing
Table 11: Practical Example for Clarity grading
Total wt A-BL SI I D REC. COLOURED TOTAL Shaft
2095.93 73.64 84.37 1680.03 152.43 NIL 104.69 2095.16 ROM
585.38 49.33 36.23 447.56 - - 52.13 585.25 MAIN
Source: TMAA
Explanation based on the above practical example
D and Coloured already discussed on cobbing.
A-BL: These are the tanzanite and other gemstones without
inclusions and
they mean A, B and BL. These go direct to colour grading without
passing to
Sizing 1.
SI: These are the gemstones with Slight Inclusion. They may be
A, B or BL with
inclusions. (ASI, BSI and BLSI) but these naming will be
arranged on colour
grading.
I: These are the gemstones with real inclusions vividly seen.
They may be A, B
or BL with vivid inclusions (AI, BI and BLI). But these colours
will be
categorized during colour grading;
After that SI and I go to Sizing 1 to be graded according to
their sizes from the range of
size1-14 and where;
The SI and I with sizes 1-4 (0.01 - 0.49g) are packed ready for
selling.
Those from size 5-14 (0.5 - 20+g) go to Colour grading and then
to sizing
2.
Generally at Clarity process, you will have three groups of
Tanzanite
A, B and BL without inclusions
A, B and BL with Slight Inclusion (SI), that is ASI, BSI and
BLSI and finally
A, B and BL with vivid Inclusion (I) that is AI, BI and BLI
The figure shows the clarity grading by using fiber light to
identify the level of
inclusions on and within the gemstones. The figure also shows
the three containers
in which those three types of Tanzanite are stored during the
process.
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2009 Freelance Writing
Figure 11: Clarity grading by using fiber light
6.6 Sizing Indicator
In gemstone sizing refers to arrangement of gemstones according
to their weights,
inclusions and colours. There are two types of arrangements of
gemstones during
processing;
Sizing one (1) and Sizing two (2).Conversional weight is 0.2g
equals to 1 carat (1ct)
Sizing one (1): This involves arrangement of gemstones from size
1-14.Those
from size 1-4 are collected and packed ready for selling and the
gemstones
above size 5-14 are taken to Colour grading and then finally to
Sizing two(2)
Sizing two (2): This deals with gemstones from size 5-14 and is
the final
process. Though due to human error you may find the gemstones
with sizes
below 5-14
Below is the table (Table 11) showing the Sizing Indicator (the
range of weight and
corresponding size)
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2009 Freelance Writing
Table 12: Sizing Indicator used at TanzaniteOne
SIZE ROUGH WEIGHT(g) GRADE
1 0.01 0.09 B/BL
1 0.01 0.15 C
2 0.10 0.15 B/BL
2 0.16 0.19 C
3 0.20 0.29 B/BL/C
4 0.30 -0.49 A/B/BL/C
5 0.50 0.79 A/B/BL/C
6 0.80 0.99 A/B/BL/C
7 1.00 1.99 A/B/BL/C
8 2.00 2.99 A/B/BL/C
9 3.00 4.99 A/B/BL/C
10 5.00 6.99 A/B/BL/C
11 7.00 9.99 A/B/BL/C
12 10.00 14.99 A/B/BL/C
13 15 .00 19.99 A/B/BL/C
14 20+ A/B/BL/C
Souce: TanzaniteOne Mining Company Ltd.
6.7 Sizing One (1)
This deal in essence with the gemstones having inclusions .All
gemstones with
inclusions are arranged at Sizing One with relation to their
weight. Those without
inclusions are not involved at Sizing one they are direct taken
to Colour grading and
Sizing two.
Remember at clarity process, the gemstones without inclusions
(A, B, BL) were taken
to colour grading and then to Sizing two without passing into
sizing one.SI and I
gemstones are the ones taken into Sizing one.
Table 13: Practical Example for Sizing 1
Total wt Size 1 Size 2 Size 3 Size 4 Size 5-14 Total grade
Shaft
770.50 50.07 42.17 175.96 266.98 234.36 770.17 I ROM
85.49 - - - 10.65 74.81 85.46 SI CT
36.23 - - - 5.58 30.65 36.23 SI MAIN
143.77 1.71 4.12 26.62 55.84 55.40 143.69 I DELTA
21.98 - - 0.54 5.28 16.07 21.89 SI DELTA
Source: TMAA
Explanation based on the above practical example
Size1 to Size 4: The gemstones with inclusions and having weight
from 0.01-
0.49g that is size 1-4 are finalized/packed for Selling. The
reason is that, they
are two small for further processes like Cutting .The only
further process is heat
treatment to make them more Blue violet.
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2009 Freelance Writing
Size 4 to Size 14: Those with weight from 0.5-20+g that is Size
5-14 are taken
into Colour grading then to Sizing two. These can be further
treated
(cutting/polishing) therefore is better to grade them up to the
final stage (Sizing
two) and the buyer will decide whether to buy rough or further
treatment
(cutting/polishing).
Figure 12: Sizing One (1) process
Each beaker holds one size of gems that is size 1, 2, 3 and 4
its own beaker. While
sizes 5 up to 14 are mixed in one beaker (see the one full to
the rim). At the left hand
side on the figure is the scale used for sizing (weight
ranges)
6.8 Colour grading
This is the most complex process in grading Tanzanite and other
gemstones. This can also be used as a loophole for tax deviations.
Blue colour can be called Blue light purposely to decrease the
value. Therefore the evaluators and buyers need time to cross check
them though roughly to confirm the colour. But as I said the
peripheral between Blue and light blue sometime not easy to mark.
The same happen between Blue Light Slightly Included and Blue
Slightly Included. These ambiguities were mitigated by Munsell when
he introduced the concept of hue (original colour) saturation
(intensity) and tone (lightness/darkness).
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2009 Freelance Writing
Saturation and Tone are used to distinguish the range of colors
(range of hue) is it deep Blue, pure Blue or slightly Blue. Hue
doesnt confuse because is the color that we notice immediately like
red, blue, yellow, or green. Albert H. Munsel, an American painter
and art instructor was the first to identify these basic qualities
of a specific color - hue, saturation and tone. The GIA eventually
adopted these principles to create a standardized gemstone
color-grading system.
But the system has no final guidelines to base; it just gives
you the blueprint of the system principles and where to start but
how to finalize depends on the beauty of the beholder. Regardless
of the shortcomings of GIA, it is still the only System to be
referred. The figure 9, 10 and 11 will help us to build the concept
of saturation and tone before we go into practical example.
Figure 13: Gemstone Hue Chart
Saturation is the intensity of the hue present in a color
sensation. Colors of low
saturation are sometimes called weak, grayish or brownish while
those of high
saturation are said to be highly saturated, strong or vivid.
Figure 14: Gemstones Saturation chart
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2009 Freelance Writing
Tone indicates the lightness or darkness of a color sensation.
The scale ranges from 0
for pure black to 10 for pure white. Black and white and the
grays between them are
called neutral colors. They have no hue. Colors that have a hue
are called chromatic
colors. Colors that do not have a hue are known as achromatic.
The value scale
applies to chromatic as well as to neutral colors. GIA uses 7 of
those steps (Tones 2
thru 8) for grading tone in transparent colored gemstones.
Figure 15: Gemstone Tone chart
NOTE: From the above concepts of Hue, Saturation and Tone, one
can still get stuck
to distinguish between Saturation and Tone. Am I wrong? And
still no quantitative
techniques to mitigate the confusion.
6.8.1 GIA Colour grading steps
Judge hue and saturation by identifying the Key Colors which are
direct seen. We do
that by face up stone and find the Key colors - the colors under
the crown facets which
show the best representation of color in the stone. The fiber
light is used to assist to
identify the colour satisfactorily. We do not consider washed
out, windowed, or areas
of extinction;
Windowing refers to the washed out area in the center of a
stone
generally seen through the table. A stone with a large washed
out area is
said to have a large window.
Extinction refers to the areas of darkness visible through the
crown.
These areas appear gray or black.
Brilliance is a measure of the light which enters the stone and
reflects
back to our eye. It is seen as the bright areas or flashes
within the stone.
You may see these steps; they just explain how to start but dont
comment how to arrive
to the final judgment. The Crown, Window /table, girdle these
can be seen after cut but
for rough gemstone not ease to know the crown and window sides.
These are
shortcomings of GIA.
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2009 Freelance Writing
6.8.2 TanzaniteOne Colour grading steps
Tanzanite Gemstones are arranged according to the standard
colour. People do
confuse Colour grading with clarity grading .During clarity
grading, the criteria is to
look on the inclusions only, grade those without inclusions and
those with inclusions
regardless of their colour. While Colour grade is based on
colour, weight and
inclusion.
Here the standard colour has already implemented. Blue colour is
a Key Colour in
grading all gemstones available at TanzaniteOne. Tanzanite is
predominantly Blue and
brown. When heated it turns Blue-Violet permanently. Tsavorite
is greenish and
Coloured gemstones are pale blue and pale brown. Tsavorite is
separated but the rest
are graded based on blue colour. There are A, B, BL, BSI, BLSI,
BI and BLI types of
colour. Those gemstones which are not blue are named after blue
colour as I said
before. Suppose the gemstone is brown or yellow it will be named
as Blue, B and if
slightly brown/yellow it will be named Blue light, BL etc
For beginners, the Master stones or Master colours are used to
differentiate the
colour until the grader become experienced with those colours
and start doing grading
in his/her own.
Table 14: Practical example for Tanzanite Colour grading at
TanzaniteOne
Total wt A B BL COLOUR YELLOW WASTE TOTAL Shaft
470.12 - 88.87 362.67 18.51 - - 470.05 CT
119.72 - 20.68 86.79 12.39 - - 119.86 DELTA
Source: TMAA
Master colours referred for tanzanite
COLOURED BL B A
Explanation based on the above practical example
A: Is the exceptional colour, deep Blue without inclusions. Very
rare to get it.
B: Blue or Brown or any visible colour
BL: Blue light or Brown light or any light colour
Colour: Pale Blue, Brown or any pale colour.
The same process as for Clarity grading is used and also fiber
light is used (refer
figure)
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2009 Freelance Writing
6.9 Sizing two (2)
The intention of this section is to grade the gems according to
their weight, colour and
inclusions. We already have colour grading; the last stage is to
arrange those gems
with reference to their weight and colour. In essence Sizing two
(2) deal with gems
from Size 5 onward. Therefore expect to get more gems at Sizing
two with Size 5 and
higher. But due to human error, the gems with weight less than
Size 5 are found
taken to Sizing two stage. Thats why sometime size 1, 2, 3 and 4
appear at Sizing two
(2) stages instead of being collected at Sizing One.
Table 15: Practical Example for Sizing two (2) Total
wt
Grade SIZE
2
SIZE
3
SIZE
4
SIZE
5
SIZE
6
SIZE
7
SIZE
8
SIZE
9
SIZE
10
Total
12.79 B - - 1.32 1.61 1.89 3.20 - 4.81 - 12.83
270.18 BL 1.79 17.15 86.30 90.50 27.70 37.80 8.92 - - 270.16
16.80 BSI - - - 5.12 2.69 8.44 - - - 16.75
124.21 BLSI - - - 78.67 20.51 25.07 - - - 124.25
77.53 BI - - - 43.84 14.80 18.90 - - - 77.54
400.78 BLI - - - 343.82 40.70 16.31 - - - 400.83
31.28 B - - 0.4 1.91 6.06 9.86 - 7.10 5.94 31.27
164.69 BL - - 28.58 41.80 14.95 53.27 6.77 9.26 5.77 164.61
6.82 BSI - - - 2.95 2.45 1.30 - - - 6.70
40.05 BLSI - - - 17.61 12.33 8.00 2.01 - - 39.95
18.61 BI - - - 12.11 0.92 5.58 - - - 18.61
66.74 BLI - - - 58.04 5.07 3.61 - - - 66.72
Source: TMAA
The above can be also presented as following;
Grade Weight(g) Grade Weight(g)
4B 1.72 5B(SI) 8.07
5B 3.52 6B(SI) 5.14
6B 7.95 7B(SI) 9.74
7B 13.06 5BL(SI) 96.28
9B 11.91 6BL(SI) 32.84
2BL 1.79 7BL(SI) 33.07
3BL 17.15 8BL(SI) 2.01
4BL 114.88 5B(I) 55.95
5BL 132.3 6B(I) 15.72
6BL 42.65 7B(I) 24.48
7BL 91.07 5B(LI) 401.86
8BL 15.69 6B(LI) 45.77
9BL 9.26 7B(LI) 19.92
10BL 5.77
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2009 Freelance Writing
7.0 GEMSTONE TREATMENTS, ENHANCEMENTS, AND CARE
As critical as good cutting and polishing is, treatments have
become an integral part of the modern gemstone industry. While
these treatments are taken as commonplace within the industry, the
general public's awareness has been much lower.
Enhancements: Virtually all gem tanzanite of a blue violet color
has been heat-treated to enhance the color. In the rough state most
Tanzanite is predominantly brown and blue light. Heating at 500 to
600 degrees centigrade causes this color to change to blue. This is
a permanent and stable change.
Is The Use Of Treatments Globally Accepted ?YES, the majority of
gemstones traded internationally have undergone some form of
treatment with close to 99% of the more popular gem types being
treated. All permanent techniques are universally accepted. Are All
The Treatments Used Permanent? Except for Emeralds that are treated
with colorless oil or polymers, most gemstone treatments are
permanently stable with normal wear.
Care of Tanzanite Gemstones. Due to Tanzanite's relative
softness, it should be treated with respect. It is not a gem
that should break easily but due to its relatively low score on
the Mohs Scale (6) it can scratch more easily than other gems like
Ruby. To clean it does not use an ultrasonic cleaner or steam
cleaner often found in jewelers. The best method is simply to use a
toothbrush and warm, soapy water. Similarly, when setting your
Tanzanite gem your jeweler should realize that he should be careful
and not use undue levels of heat. Table 15 shows the treatment
methods of different gemstones.
PUBLIC POINTS OF
INTEREST TO BE
ADDRESSED
Few people who know that
Tanzanite is heated to get Blue
violet colour. This treatment
increases the value of tanzanite
like Cuts of tanzanite did.
IF THAT IS THE CASE
The Government has posed a ban
of cutting the Tanzanite abroad.
What about the heat treatment?
TUCSON TANZANITE
PROTOCOL
The purpose of the protocol is to
safeguard the Tanzanite from
dirty hands!! Do the protocol
under control of all shareholders
who signed it or is only now
under control of the
TanzaniteOne who only care
about the Sales regardless of who
buy the tanzanite?
By
Compiler
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2009 Freelance Writing
8.0 GEMSTONES CUT AND POLISH
Second Compilation will include this process of Tanzanite
cutting techniques in details. For now just have some partial hints
of cutting techniques.
The process of cutting and polishing gems is called gemcutting
or lapidary, while a person who cuts and polishes gems is called a
gemcutter or a lapidary. Gemstone material that has not been
extensively cut and polished is referred to generally as rough. All
gems are cut and polished by progressive abrasion using finer and
finer grits of harder substances. Diamond, the hardest naturally
occurring substance is used as an abrasive to cut and polish a wide
variety of materials, including diamond itself.
8.1 Cutting Techniques
Several common techniques are used in lapidary work: Sawing,
grinding, sanding, lapping, polishing, drilling and tumbling.
Sawing: A thin circular blade usually composed of steel, copper,
or a phosphor
bronze alloy impregnated along the outer edge with diamond grit
and rotating at
several thousand surface feet per minute literally scratches its
way through a
gemstone.
Grinding: with silicon carbide wheels or diamond-impregnated
wheels,
gemstone is shaped to a desired rough form, called a
preform.
Sanding is similar to grinding but uses finer abrasives. Its
purpose is to remove
deep scratches left by coarser abrasives during grinding.
Lapping is very similar to grinding and sanding, except that it
is performed on
one side of a rotating or vibrating flat disk known as a lap,
and it is used
especially to create flat surfaces on a stone (as in
faceting).
Polishing: After a gemstone is sawed and ground to the desired
shape and
sanded to remove rough marks left by coarser grits, it is
usually polished to a
mirror-like finish to aid light reflection from the surface of
the stone or
refraction through the stone, in the case of transparent
materials.
Tumbling: Large quantities of roughly shaped stones are often
tumbled, i.e.,
turned at a slow speed in a rotating barrel with abrasives and
water for
extended periods of days or weeks. By tumbling with
progressively finer grades
of abrasive and washing carefully between grades, the stones are
gradually
smoothed and polished.
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2009 Freelance Writing
Cabochons: One of the simplest lapidary forms is the cabochon, a
stone that is
smoothly rounded and polished on top, relatively flattish, and
either flat or
slightly rounded on the bottom. This form of cutting is often
used for opaque or
translucent stones, but is also frequently used for transparent
materials that
contain too many inclusions to yield a good faceted stone.
Coloration and
patterning provide the major interest in such stones.
Faceted Stones: Faceting is most often done on transparent
stones. Flat facets
are cut and polished over the entire surface of the stone,
usually in a highly
symmetrical pattern.
Inlays: In an inlay, a gemstone is cut to fit and glued into a
hollow recess in
another material (metal, wood, or other stones) and then the top
ground and
polished flush with the surrounding material.
Intarsias and Mosaics: In both intarsia and mosaic work, small
bits of different
colored stones are fit together and the top cut and polished to
present a picture
or other interesting pattern
Sculpture: Gemstones can be carved, like other materials, into
almost any
form, limited only by the talents of the sculptor. Carving is
accomplished with a
variety of diamond-impregnated steel bits.
9.0APPENDICES
Appendix 1: Birthstones & Anniversary Gemstones
Month Gemstone
Jan Garnet
Feb Amethyst
Mar Aquamarine
Apri Diamond
May Emerald
June Alexandrite
July Ruby
Aug Peridot
Sept Sapphire
Oct Opal, Pink Tourmaline
Nov Topaz
Dec Tanzanite
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2009 Freelance Writing
Appendix 2: Anniversary Gemstones
Year Gemstone
1st Remembrance or Gold
2nd Remembrance or Garnet
3rd Remembrance or Pearl
4th Remembrance or Blue Topaz
5th Remembrance or Sapphire
6th Remembrance or Amethyst
7th Remembrance or Onyx
8th Remembrance or Tourmaline
9th Remembrance or Lapis Lazuli
10th Remembrance or Diamond
11th Remembrance or Turquoise
12th Agate or Jade
13th Citrine or Moonstone
14th Opal or Moss Agate
15th Ruby or Rock Crystal
16th Peridot or Topaz
17th Amethyst
18th Garnet or Cats Eye Chrysoberyl
19th Aquamarine, Rose Quartz, or Rhodochrosite
20th Emerald or Jade
21st Iolite
22nd Spinel
23rd Imperial Topaz
24th Tanzanite
25th Silver Jubilee
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2009 Freelance Writing
30th Pearl Jubilee
35th Emerald, Coral, or Jade
40th Ruby
45th Sapphire
50th Gold Jubilee
55th Emerald or Alexandrite
60th Diamond Jubilee
65th Blue Spinel
70th Sapphire Jubilee
75th Diamond Jubilee
80th Ruby Jubilee
Appendix 3: Weekday
Sunday ~ Golden Topaz, Sunstone, Amber
Monday ~ Pearl, Moonstone, Rock Crystal
Tuesday ~ Ruby, Emerald, Star Sapphire, Garnet
Wednesday ~ Amethyst, Lodestone, Star Ruby, Turquoise, Sapphire,
Lapis Lazuli
Thursday ~ Sapphire, Carnelian, Amethyst, Cat's Eye
(Chrysoberyl)
Friday ~ Emerald, Cat's Eye (Chrysoberyl), Alexandrite, Agate,
Malachite
Saturday ~ Diamond, Turquoise, Labradorite
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2009 Freelance Writing
10: REFERENCES
1. UNDP, 1998 World Report on Gemstones Mining.
2. TMAA Database. http://www.tmaa.go.tz
3. How are gems cut and polished.
http://www.tradeshop.com/gems/howcut.html
4. Conrad Mtui, TMAA TanzaniteOne Analytical Report ,2011
5. Physical and optical properties of Minerals and gemstones.
http://www.rocksinmyheadtoo.com/PhysOpti.htm
6. The gemstones cutting process.
http://www.gemstoneartist.com/Process.asp
7. Understand tanzanite GIA colour grades.
http://www.lapigems.com/tanzanite.asp
8. Tanzanite unique properties.
http://www.etanzanite.com/tanzanite_pictures.htm