Matter and Minerals. Minerals: Building blocks of rocks Naturally occurring Solid Inorganic Definite chemical composition Crystal structure due to internal.

Matter and Minerals

Minerals: Building blocks of rocks

• Naturally occurring• Solid• Inorganic• Definite chemical

composition• Crystal structure due

to internal arrangement of atoms

http://www.minerals.net/gemstone/index.htm

General Facts about Minerals

• Between 2 - 3,000 have been identified

• A few are “native elements” -- made of only one element, such as sulfur, gold. copper, and graphite (carbon)

• Most are compounds, especially the silicate group (Si, O).

• Other important groups are oxides, carbonates, and sulfides.

Less than a dozen are common in most rocks

• Quartz• Feldspar (group)• Muscovite (white

mica)• Biotite (black mica)• Calcite• Pyroxene

• Olivine• Amphibole (group)• Magnetite, limonite,

and other iron oxides• Pyrite

How do we identify minerals?

• Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other

Physical Properties of Minerals

• Color:– Most obvious, but often misleading

– Different colors may result from impurities

Example:Quartz

A mineral can be many different colors. Below is Mica.

Many minerals can be the same color. Below are gold colored minerals. Which

one is gold?


• Color: Streak – color of a mineral in powdered form

(used for metallic minerals)

Obtained by scratching a mineral on a piece of unglazed porcelain.

Example:Hematite

Gold

• When gold is run across a streak plate it makes a yellowish-gold color.

Pyrite or “Fool’s Gold”

• When pyrite is run across a streak plate, it has a black or dark green streak.

• Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.

Hematite• Hematite’s color is

grey, but its streak is red.

• Hema means blood. • The mineral was

named hematite because it looked like it was bleeding when it was taken across a streak plate.


• Luster:– How a mineral surface reflects light

– Two major types:

• Metallic luster

• Non-metallic luster

Metallicexample:Galena

Non-metallicexample:

Orthoclase

Pyrite has metallic luster

Quartz has vitreous luster


• Hardness:– How easy it is to scratch a mineral– Mohs Scale of Hardness

• relative scale

• consists of 10 minerals, ranked 1 (softest) to 10 (hardest)

Mohs Scale of Hardness

Hardest (10) – Diamond

Softest (1) – Talc

Common objects:

- Fingernail (2.5) - Copper coin (3.5) - Wire nail (4.5) - Glass (5.5) - Streak plate (6.5)

Gypsum is soft, it can be scratched by a fingernail.

Calcite is soft, but a little harder because it cannot be scratched by a

fingernail, but it can be scratched by a coin

Fluorite is harder. It can be scratched by a nail, but not a coin or fingernail.

Diamond is the hardest mineral, so it scratches every mineral.


• Crystal shape (or form):– external expression of a mineral’s internal

atomic structure

– planar surfaces are called crystal faces

– angles between crystal faces are constant for any particular mineral

Quartz Pyrite


• Cleavage vs. Fracture:– The way a mineral breaks

– Cleavage: tendency of a mineral to break along planes of weakness

– Minerals that do not exhibit cleavage are said to fracture

Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.


• Cleavage is described by:– Number of planes– Angles between adjacent planes

– These are constant for a particular mineral


• Cleavage (1 direction):

Example: mica


• Cleavage (2 directions):

orthoclase

amphibole



halite

calcite



fluorite


• Fracture:– minerals that do not exhibit cleavage are said to

fracture

– smooth, curved surfaces when minerals break in a glass-like manner: conchoidal fracture

Quartz


• Specific gravity:– weight of a mineral divided by weight of an

equal volume of water

– metallic minerals tend to have higher specific gravity than non-metallic minerals

GalenaSG=7.5

QuartzSG=2.67

Mineral properties

• PHYSICAL CHARACTERISTICS: Specific Gravity S.G. is an easily measured physical property that can be readily estimated. In general,

sulphides and oxides have much higher specific gravities than silicates.

MINERAL GROUP MINERAL SPECIFIC GRAVITY

Framework Silicate Quartz 2.6-2.7

Framework Silicate Feldspar 2.6-2.7

Sheet Silicate Mica 2.8-3.0

Chain Silicate Amphibole 2.9-3.2

Chain Silicate Pyroxene 3.2-3.6

Isolated Silicate Olivine 3.3-4.4

Isolated Silicate Garnet 3.5-4.4

Sulphide Sphalerite 4.0

Sulphide Chalcopyrite 4.2

Sulphide Pyrite 5.0

Oxide Magnetite 5.2

Oxide Hematite 5.3

Sulphide Galena 7.2

Oxide Pitchblende 9.5

Element Native Gold 12.4

– reaction with hydrochloric acid (calcite fizzes)


• Other properties:

– taste (halite tastes salty)

– feel (talc feels soapy, graphite feels greasy)

– magnetism (magnetite attracts a magnet)

• Rock-forming minerals– ~30 common minerals make up most rocks in

Earth’s crust

– Composed mainly of the 8 elements that make up over 98% of the crust

Mineral Groups

Mineral Groups

All others: 1.5%

Element Abundances

SilicaSilica(SiO(SiO44))4-4-SILICATES

Common cations thatbond with silica anions

mineral formula cleavage Silicate structureOlivine (MgFe)2SiO4 none Single

tetrahedronPyroxene (Mg, Fe) SiO3 two cleavage

planes at 900

chains

Amphiboles:Eg. hornblende

(Ca2Mg5)Si8O22(OH)2 Two planes at 600and 1200

Double chains

Mica Muscovite

KAl3Si3O10(OH)2 One plane sheets

Biotite K(MgFe)3Si3O10(OH)2

Feldspars:K-feldsparOrthoclase, microcline

KAlSi3O8 Two planes at 900 Three dimensional networks

Plagioclase (Ca,Na)AlSi3O8

Quartz SiO2 none Three dimensional network

Common Silicate mineral groups

group member formula usesOxides

Sulphides

Sulfates

Native elements

Halides

Carbonates

MagnetiteHaematiteCorundum

GalenaSphaleritePyrite

GypsumAnhydrite

GoldSilverCopperSulfurGraphite

HaliteFlourite

Calcite

Fe3O4

Fe2O3

Al2O3

PbSZnSFeS2

CaSO4.H2OCaSO4

AuAgCuSC

NaClCaF2

CaCO3

Ore of ironOre of ironAbrasive

Ore of leadOre of zincFool’s gold

Used for plaster

Precious metalPrecious metalUsed for WiresUsed in chemicalspencils

Common saltUsed in chemicals

Used in cement

Common Non Silicate mineral groups

– Oxides O2-

– Carbonates (CO3)2-

– Sulfides S2-

– Sulfates (SO4)2-

– Halides Cl-, F-, Br-

– Native elements (single elements; e.g., Au)

Mineral Groups

• Silicates (most abundant)

• Non-silicates (~8% of Earth’s crust):

Mineral Groups – Silicates

• Silicates– Tetrahedron

• fundamental building block

• 4 oxygen ions surrounding a much smaller silicon ion

Silicon-oxygentetrahedron

(SiO4)4-


• Joining Silicate Structures

– How tetrahedra may be linked:

• independent tetrahedra

• single chains

• double chains

• sheets

• 3-D framework

Mineral Groups– Silicates –

Olivine Groupdark silicates (Fe-Mg)


No cleavage

ferromagnesian

The Olivine group is composed of three minerals, with the following formulas:Forsterite = Mg2SiO4

Olivine (Chrysolite) = (Mg,Fe)2SiO4

Fayalite = Fe2SiO4

The intermediate variety, Olivine, is not scientifically recognized as a separate mineral, but is nevertheless mentioned.

Magnesium iron silicate. The series ranges from the magnesium end member, Forsterite, through the intermediate member, Olivine (also known as Chrysolite), to the iron end member, Fayalite

Composition

Color Olive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, white

Streak Colorless

Hardness 6½ - 7

Crystal Formsand Aggregates

Usually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses.

Transparency Transparent to translucent

Specific Gravity 3.2 - 4.2

Luster Vitreous

Cleavage none

Fracture Conchoidal

Tenacity Brittle

http://www.minerals.net/glossary/terms/g/grain_a.htm

http://www.minerals.net/glossary/terms/g/grainy.htm

Uses The variety Peridote is a famous gem. It creates a distinctive, yellow-green to olive-green gem that is well known. It is the birthstone for August.

Olivine is also used as a flux for making steel, and is an ore of magnesium.

Striking Features Color, localities, and hardness

Complex Tests Soluble in hydrochloric acid

Pyroxene GroupFerromagnesian / dark silicates (Fe-Mg)


2-directionsof cleavage(at nearly 90 degrees)

Augite

MineralsThe typical pyroxene structure

contains chains of SiO3

tetrahedrons

• The slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90o degrees (actually 93o and 87o).

Pyroxene minerals are common in in meteorites and the extrusive igneous rock called basalt. There are many different types of pyroxene including augite, wollastonite, diopside, enstatite, and hypersthene. All of the types contain Si2O6 but some have sodium (Na) while others have iron (Fe), magnesium (Mg), or a combination of these three elements . The general properties of the more common pyroxene minerals, such as augite, are listed below.Shape:Orthrorhombic or MonoclinicLuster: Glassy or metallic Color: Black Streak: White, light green or light brown Hardness: 5-6.5 on Mohs hardness scaleCleavage: Two planes that meet at nearly a 90-degree angle Fracture: Most have uneven and brittle fractures.

Amphibole GroupFerromagnesian / dark silicates (Ca, Fe-Mg)


2-directionsof cleavage(not at 90 degrees)

Hornblende

There are several different minerals within the amphibole group, but the most common type is hornblende. You can find small crystals of hornblende in many types of igneous rocks. They often look like little dark specks. Hornblende (Ca2Mg5)Si3O22(OH)2

Shape: Monoclinic (crystals look like short, six-sided columns) Luster: Glassy or milkyColor: Black or dark green, translucent to opaqueStreak: Grey-green or grey-brownHardness: 5-6Cleavage: Two planes that meet at a 124-degree angleFracture: Uneven brittle fracture

Mica Group and Clay Mineralslight silicates (K, Al)


1-directionof cleavage

Muscovite

non-ferromagnesian

Minerals• Micas and Clay Minerals

• Sheets of tetrahedra are the building blocks. Aluminum is also involved in thesesheet structures which are charge-balanced by the cations Mg, Na and K.

• most common mica minerals:muscovite , biotite

Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book.

BiotiteK(MgFe)3Si3O10(OH)2

•Shape: Monoclinic. Forms flat plates. •Luster: Pearly, metallic•Color: Dark brown, dark green or black •Streak: White•Hardness: 2.5-3•Cleavage: Yes, •one plane of cleavage •Fracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks.

MuscoviteKAl3Si3O10 (OH)2

•Shape: Monoclinic. Forms flat plates. •Luster: Pearly, metallic •Color: Colorless or lightly tinted •Streak: White •Hardness: 2-3 on Mohs Hardness Scale•Cleavage: Yes, one plane of cleavage •Fracture: This mineral is also flexible and doesn’t fracture very easily.

Feldspar Grouplight silicates (K-Na-Ca, Al)


2-directionsof cleavage

(at 90 degrees)

Orthoclase

Plagioclase

K-feldspar

Ca/Na-feldspar

Most common mineral group

Minerals• Feldspar group

• A second group of alumino-silicates, tetrahedra form three-dimensional frameworks with Ca, Na and K as the balancing cations.

• The very abundant

• feldspar are K-Na bearing alkali

The K-feldspars or alkali felspars:

•Microcline, (Potassium aluminum silicate) •Orthoclase, (Potassium aluminum silicate)

Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous rocks like granite where the crystals look white or pink. There are several types of feldspar. The characteristics of the two most common types are listed below. These two common types of feldspar are difficult to tell apart besides their color. Color can be helpful, but beware because the same mineral can often have different colors. The sure way to tell these two apart is by looking at the crystal surfaces for thin parallel groves called striations. Plagioclase feldspar has striations but orthoclase feldspar does not.

Orthoclase K AlSi3O8

•Shape: Monoclinic (Flat tabular or prism-shaped crystals)•Luster: Glassy or pearly •Color: Cream to pink •Streak: White •Hardness: 6 on Mohs Hardness Scale•Cleavage: perfect •Fracture: brittle Plagioclase CaNaAlSi3O8

•Shape: Triclinic (Single prism-shaped crystals are very rare. You are much more likely to find many crystals that have grown together in a mass. •Luster: Glassy or pearly •Color: White to gray •Streak: White •Hardness: 6-6.5•Cleavage: perfect •Fracture: brittle

Quartzlight silicates (pure SiO2)


no cleavage(conchoidal fracture)

hard, resistant to weatheringQuartz

Quartz is one of the most common mineral in Earth’s crust! Silica (Si) and Oxygen (O) are the only elements within pure quartz. Quartz can be found in all sorts of rocks. Most sand is made of quartz because it is hard and does not weather away easily. Some pieces of quartz are white like milk but most are clear like glass, sometimes with a little pink or grey tinge of color.QuartzShape: Trigonal (Perfect crystals are usually 6-sided prisms with a pyramid shape at the end. However, it is much more common to find many crystals that have grown in a mass or broken crystals.) Luster: vitreousColor: Colorless or white. Some varieties are pink or smoky. Streak: White Hardness: 7Cleavage: None Fracture: Conchoidal

Minerals• Quartz

• Silica tetrahedra alone can form a neutral three-dimensional framework structure with no need for other cations.

This arrangement forms a very stable structure

popular as ornamental stone and as gemstones•Amethyst is the purple gemstone variety. •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst. •Milky Quartz is the cloudy white variety. •Rock crystal is the clear variety that is also used as a gemstone. •Rosey Quartz is a pink to reddish pink variety. •Smoky quartz is the brown to gray variety.

Mineral Groups

FerromagnesianSilicates (Fe, Mg)

Non-ferromagnesianSilicates (K, Na, Ca, Al)

OxidesCarbonatesSulfides/sulfatesNative elements

MineralsThere are a few important groups of non-silicate minerals.

Only the carbonates are significant as rock-forming minerals. The remaining mineral groups are often ore minerals and provide economic sources for various elements.

The important non-silicate groups are: – Carbonates

– Evaporites

– Oxides

– Sulphides

– Phosphates

Non silicates:

• Carbonates Co3

• The important carbonates are the minerals calcite and dolomite. Both are significant rock-forming minerals.

• The calcite group

• Calcite (Calcium Carbonate)

• Magnesite(Magnesium Carbonate)

• Rhodochrosite (Manganese Carbonate)

• Siderite(Iron Carbonate)

• Smithsonite (Zinc Carbonate)

Minerals

MineralsNon silicates:

• Evaporites: including the minerals halite, and fluorite; Sulphates including the minerals gypsum and anhydrite.

The most famous halide mineral, halite (NaCl) or rock salt


• Evaporites

•Fluorite: CaF2, Calcium Fluoride


•Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate


• Oxides

• oxides (hematite and magnetite) Fe2O3, Iron Oxide

• hydroxides (limonite and goethite)

• important minor constituents in rocks.

• aluminum oxide bauxite can also occur as a rock-forming mineral.

• oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium.


• Sulphides

• The mineral pyrite is the only sulphide that occurs commonly in rocks.

• Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc.

• FeS2, Iron Sulfide


• Sulphides

• The mineral pyrite (FeS2) is the only sulphide that occurs commonly in rocks.

• Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc.

• Galena, Chalcopyrite

http://mineral.galleries.com/minerals/sulfides/class.htm


• Phosphates are relatively rare. The only important phosphate mineral is apatite.

• Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate

Common minerals• the most common minerals you'll find in rocks (rock

forming minerals)• This pile contains plagioclase feldspar, potassium feldspar, quartz

, muscovite mica, biotite mica, amphibole, olivine, and calcite.

2.www.earth2class.org/er/students/Minerals.ppt

1.www.specialconnections.ku.edu/.../cs/.../caseb_rocks_minerals.ppt –

3.www.lwr.kth.se/Grundutbildning/AE2401/.../review%20minerals.ppt

4.www.sci.uidaho.edu/geol111/Geology%20101/minerals_II_jh

Acknowledged sources

Matter and Minerals. Minerals: Building blocks of rocks Naturally occurring Solid Inorganic Definite chemical composition Crystal structure due to internal.

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