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Mineralogy & Petrography
QAB1034Lecture #2
QAB1034 Mineralogy & Petrography
Geoscience & Petroleum Engineering Department
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Learning Outcomes
Students should be able to:
Identify various categories of minerals
through their physical properties.
eren a e e ween w nn ng, c eavage,fracture, hardness, SG, streak
and origin.
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Physical Properties of MineralsThese are the physical properties
most
useful for mineral identification: Colour
Luster
Transparency
Crystal Systems
Crystal Habits Twinning
Cleavage
Fracture
Hardness
Specific Gravity
Streak
Associated Minerals
Notable Localities
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Habit: Terms
Acicular, Capillary, Filiform, Bladed,
Dendritic, Radiating, Drusy, Fibrous
Globular, Colloform, Foliated, Micaceous,
, ,Granular, Columnar, Prismatic
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Acicular
Slender, needle-like crystals: tourmaline,
hornblende, arsenopyrite, rutile, apatite,sillimanite;
selenite
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Capillary and filiform
hair-like or thread-like: native Au, Ag, Cu
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Bladed
elongated crystals flattened like a knife
blade: kyanite, tremolite
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Dendritic
arborescent, in slender divergent
branches, somewhat plantlike--nativemetals, pyrolusite
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Radiating
divergent: zeolite; tremolite; talc
pyrolusite, tourmaline
Tremolite
Tourmaline
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Drusy
surface covered with a layer of small
crystals--sugar like: calcite, quartz,sphalerite, pyrite
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Fibrous
chrysotile asbestos
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Globular and colloform
radiating individuals forming small
spherical groups
examples include zeolites, quartz,
, , ,
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Botryoidal
bunch of grapes, example: heamatite,
pyrolusite
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Reniform
kidney like, examples hematite, malachite
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Mammillary
Very large, example is malachite
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Foliated
easily separable into plates or leaves:
tremolite; hematite; graphite
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Micaceous
similar to foliated but splits into very thin
sheets: muscovite, biotite, chlorite
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Tabular or lamellar
flat and platelike: barite, dolomite
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Granular
composed of many individual grains of
similar size: olivine, garnet
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Prismatic or columnar
elongated crystals with identical faces
parallel to a common direction: tourmaline,hornblende,
apatite
Green tourmaline
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Twinning
Crystals that are related to one another by
some geometric relation.
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Simple or Contact twins
e.g. the fish tail of gypsum
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Penetrative
e.g. Carlsbad in Orthoclase
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Polysynthetic (multiple)
e.g. Plagioclase
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Cyclic
e.g. aragonite
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CLEAVAGE AND PARTING
Cleavage is the easy
breakage of a mineralalong a plane surfaceor plane of
weakness.
the perfect cleavagein mica, which isparallel to 001.
Parting occurs alongtwin planes
Augite
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Parting
Occurs when a mineral breaks along a
twin plane, e.g. augite
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TYPES OF MINERAL CLEAVAGEPerfect: Very good
breakage and the new
surfaces are shiny, e.g.muscovite.
Distinct: New surfaces
irregular steps, e.g.orthoclase.
Indistinct: Generallyrough with only a few
planar areas (generallynot useful) e.g.corrundum.
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PROBLEMS WITH MINERAL
CLEAVAGE
Confusion between cleavage and faces
Numbers of cleavages
Intersection of cleavages
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FRACTURE
Terms that are used
to describe fractureare:Conchoidal: quartz
Hackly: jagged and sharp
Fibrous and splintery
Uneven or irregular: rough
& irregular surfaces
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Conchoidal
An example of obsidian
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MOHS HARDNESS SCALE This is a mineral's resistance
to scratching. It is a relative
scale. Minerals with highernumbers will scratch mineralsbelow
them on the scale.
1. Talc
. ypsum
3. Calcite4. Fluorite
5. Apatite
6. Orthoclase
7. Quartz8. Topaz
9. Corundum
10. Diamond
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SPECIFIC GRAVITY
This is the ratio of the density of the
mineral to the density of water. It isdimensionless quantity.
Substances with a
denser than water
Weight Air/(Weight Air-Weight in water) =
specific gravity (SG), orSG = substance/water
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SPECIFIC GRAVITY
Increases with increasing atomic weight of the cation.
For example in the orthorhombic carbonates:
Aragonite CaCO3 Ca 40 2.95
Strontianite SrCO3 Sr 87 3.76
Witherite BaCO3 Ba 137 4.29
Cerrusite PbCO3 Pb 207 6.55
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Streak Colour Streak is the colour of the
powder of mineral, obtained by
drawing the mineral across theunglazed porcelain
streakplate.
The trail of finely groundpow er genera y as a more
consistent characteristic color,and is thus an
importantdiagnostic tool in mineralidentification.
Streak is particularly important
as a diagnostic for opaque andcolored materials, not forsilicate
minerals.
Hematite
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Notable Localities
Muscovite Russia
Dolomite Italy
Andalusite Spain
Sarabauite Sarawak, MalaysiaMalayaite Malaysia
http://www.mindat.org/
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CONCLUSION
The twinning, cleavage, fracture,
hardness, Specific Gravity, streak colourand notable origin are
among the physical
.
Certain mineral displays a special
characteristic or properties as an
identification tool.
