Transcript
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Department of Civil and Environmental Engineering
Fareast International University (FIU)
Shubhagata Roy
Engineering Geology & Geomorphology
ROCK FORMING MINERALS
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WHAT IS A MINERAL ?
Rock Forming Minerals
A mineral, by definition, is any naturally occurring, inorganic substance, often additionally characterized by an exact crystal structure.
Its chemical structure can be exact, or can vary within limits.
Elements that occur naturally are also considered minerals.
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EXAMPLE OF MINERAL
Rock Forming Minerals
Minerals:
Quartz, Ice, Snow, Biotite, Diamond, Serpentine.
Not Minerals:
Opal, CO2, Granite, Volcanic Gas, Oil, Amber.
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MINERALOID
Rock Forming Minerals
Some natural substances that do not fulfill all the conditions given in the definition of a mineral are termed as mineraloids.
The commonest example of mineraloids is opal - a common constituent of rocks but one that is amorphous, that is, noncrystalline and without orderly internal structure.
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DIFFERENCE BETWEEN ROCK & MINERAL
Rock Forming Minerals
A mineral is a solid formation that occurs naturally in the earth.
On the other hand, a rock is a solid combination of more than one mineral formations which is also occurring naturally.
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DIFFERENCE BETWEEN ROCK & MINERAL
Rock Forming Minerals
MINERALS ROCKS
1pure
(made of same substance)more than one mineral
2 some have crystals not single crystals
3 usually pretty not usually as pretty
4 usually have a shape no definite shape
5 color is usually the same color is not the same
6 no fossils some have fossils
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IDENTIFICATION OF MINERALS
Rock Forming Minerals
Conditions to be met to be considered as minerals
Characteristics It occurs naturally as an inorganic solid.
Structure It has a specific internal structure, that is, its
constituents are precisely arranged into a crystalline solid.
Composition It has a chemical composition that varies within
definite limits and can be expressed by chemical formula.
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IDENTIFICATION OF MINERALS
Rock Forming Minerals
Conditions to be met to be considered as minerals
Physical properties It has definite physical properties (hardness,
cleavage, crystal form etc.) that result from its crystalline structure and composition.
Stability It is stable over a relatively restricted range of
temperature and pressure.
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IDENTIFICATION OF MINERALS
Rock Forming Minerals
Conditions to be met to be considered as minerals
Growth It is susceptible to chemical change; grows as
matter changes from a gaseous or liquid state to a solid state or when one solid recrystallizes to form another.
Destruction It breaks down as the solid changes back to a liquid
or gas.
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Minerals have distinguishing physical properties that in most cases can be used to determine the identity of the mineral.
The physical properties are-
1) Crystal form and habit2) Luster and Transparency3) Color and Streak4) Cleavage5) Fracture and Parting6) Tenacity7) Density8) Hardness
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Minerals may exhibit a range of crystal face development.
Euhedral – Well-developed crystal faces.Anhedral – No visible crystal faces. Usually from
growth in a confined space.Subhedral – Between the two.
Euhedral crystals - Growth in an open cavity. Anhedral crystals - Growth in tight spaces. Anhedral crystals common; euhedral rare.
1) Crystal form and habit
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
The transparency may be opaque, translucent, or transparent.
Luster refers to the general appearance of a mineral surface to reflected light.
Two general types of luster are designated as follows:
1) Metallic 2) Non-metallic
2) Luster and Transparency
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
1. Metallic
looks shiny like a metal.
Usually opaque and gives black or dark colored streak.
2) Luster and Transparency
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
2. Non-metallic
2) Luster and Transparency
Appearance Example
Vitreous looks glassy clear quartz, tourmaline
Resinous looks resinous sphalerite, sulfur
Pearly iridescent pearl-like apophyllite
Greasy appears to be covered with a thin layer of oil nepheline
Silky looks fibroussome gypsum, serpentine, malachite
Adamantine brilliant luster like diamond
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
2. Non-metallic
2) Luster and Transparency
Vitreous Adamantine
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
2. Non-metallic
2) Luster and Transparency
Pearly Resinous
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
2. Non-metallic
2) Luster and Transparency
Waxy Greasy/oily
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
2. Non-metallic
2) Luster and Transparency
Silky Dull/Earthy
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Color is fairly self-explanatory property describing the reflectance.
Metallic minerals are white, grey or yellow in color.
The presence of transition metals with unfilled electron shells (e.g. V, Cr, Mn, Fe, Co, Ni and Cu) in oxide and silicate minerals causes them to be opaque or strongly colored so that the streak, the mark that they leave when scratched on a white ceramic tile, will also be strongly colored.
3) Color and Streak
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Cleavage
Crystals often contain planes of atoms along which the bonding between the atoms is weaker than along other planes.
In such a case, if the mineral is struck with a hard object, it will tend to break along these planes.
This property of breaking along specific planes is termed cleavage.
4) Cleavage, Fracture and Parting
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Cleavage
Because cleavage occurs along planes in the crystal lattice, it can be described in the same manner that crystal forms are described.
The cleavage can also be described in terms of its quality, i.e., if it cleaves along perfect planes it is said to be perfect, and if it cleaves along poorly defined planes it is said to be poor.
4) Cleavage, Fracture and Parting
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Fracture
If the mineral contains no planes of weakness, it will break along random directions called fracture.
Several different kinds of fracture patterns are observed.
4) Cleavage, Fracture and Parting
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Fracture
Conchoidal fracture breaks along smooth curved surfaces.
Fibrous and splintery similar to the way wood breaks.
Hackly jagged fractures with sharp edges.
Uneven or Irregular rough irregular surfaces
4) Cleavage, Fracture and Parting
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Parting
Parting is also a plane of weakness in the crystal structure, but it is along planes that are weakened by some applied force.
It therefore may not be apparent in all specimens of the same mineral, but may appear if the mineral has been subjected to the right stress conditions.
4) Cleavage, Fracture and Parting
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Tenacity is the resistance of a mineral to breaking, crushing, or bending.
Tenacity can be described by the following terms-
5) Tenacity
Brittle breaks or powders easily.
Malleable can be hammered into thin sheets.
Sectile can be cut into thin shavings with a knife.
Ductilebends easily and does not return to its original shape.
Flexiblebends somewhat and does not return to its original shape.
Elastic bends but does return to its original shape.
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Density refers to the mass per unit volume.
Specific Gravity is the relative density, (weight of substance divided by the weight of an equal volume of water).
Specific gravity is often a very diagnostic property for those minerals that have high specific gravities.
SG is reflected in “heaviness” – how heavy the mineral feels.
Galena – Heavy Feldspar - Light
6) Density (Specific Gravity)
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
Hardness is determined by scratching the mineral with a mineral or substance of known hardness.
Hardness is determined on the basis of Moh's relative scale of hardness exhibited by some common minerals.
These minerals are listed below, along with the hardness of some common objects.
7) Hardness
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PHYSICAL PROPERTIES OF MINERALS
Rock Forming Minerals
7) Hardness
Hardness Mineral Common Objects
1 Talc 2 Gypsum Fingernail (2+)
3 Calcite Copper Penny (3+)
4 Fluorite
5 ApatiteSteel knife blade (5+),
Window glass (5.5)
6 Orthoclase7 Quartz 8 Topaz 9 Corundum
10 Diamond
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OTHER PROPERTIES OF MINERALS
Rock Forming Minerals
Taste Smell Effervescence Magnetism Feel Diaphaneity Piezoelectricity
Pyroelectricity Refractive Index Elasticity Malleability Ductility Sectility
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MINERAL GROUPS
Rock Forming Minerals
More than 4000 minerals have been identified. Only about 50 minerals are abundant. 98% of all minerals are made of 8 elements.
Oxygen O 46.6 %
Silicon Si 27.7 %
Aluminum Al 8.1 %
Iron Fe 5.0 %
Calcium Ca 3.6 %
Sodium Na 2.8 %
Potassium K 2.6 %
Magnesium Mg 2.1 %
All others 1.7 %
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