Download L3: Minerals and Rocks Minerals Crystallography Common Minerals

Minerals
L3: Minerals and Rocks
• Identification
• Classification
• Formation
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of common minerals & rocks
Definition:
• Highly-ordered crystalline atomic structure
• Definite chemical composition
• (Naturally occuring) homogeneous solid
Not minerals:
coal
glass
Polymorphs:
diamond (C)
graphite (C)
• Feedback on Lab 1: Rock Identification
Common Minerals to Learn
Crystallography
Olivine
Pyroxene
Amphibole
Feldspar
Quartz
Mica Biotite, Muscovite
Clay Kaolinite, Montmorillonite
Chlorite
Serpentine
Calcite & Dolomite
Gypsum
Hematite & Magnetite
Pyrite
A vast and hideously complicated subject . . .
• 32 crystal classes by symmetry elements:
rotation symmetry
rotoinversion symmetry
mirror symmetry
combinations of above
• Classes grouped into 6 crystal systems:
triclinic
monoclinic
orthorhombic
tetragonal
hexagonal
isometric
Met Ig
Sed
(Mg,Fe,Ca) Silicate
(Mg,Fe,Ca) Silicate
(Mg,Fe,Ca) Silicate + OH
(K,Na,Ca) Al-Silicate
Silica
(K,Mg) Al-Silicate + OH
Al-Silicate + OH
(Mg,Fe) Al-Silicate + OH
Mg Silicate + OH
CaCO3 & (Ca,Mg)CO3
Calcium Sulphate + H2O
Iron Oxide
Iron Sulphide
Identifying Common Minerals
1. Colour
Checklist of properties
2. Streak
Identifying Minerals: Colour White/Pale
GYPSUM
KAOLINITE
3. Lustre
QUARTZ
4. Transparency
5. Habit
CALCITE
FELDSPAR
MUSCOVITE
6. Cleavage
7. Density
8. Hardness
Identifying Minerals: Colour Dark
Identifying Minerals: Colour Green
SERPENTINE
BIOTITE
OLIVINE
PYROXENE
AMPHIBOLE
CHLORITE
Identifying Minerals: Streak
Hematite Fe2O3
Magnetite Fe3O4
Identifying Minerals: Lustre
Dull, Earthy
Milky white
Glassy
FELDSPAR
KAOLINITE
OLIVINE
QUARTZ
Irridescent, Pearly
Adamantine
MUSCOVITE
Streak: scratch the mineral on the
back of a ceramic tile and note the
colour
BIOTITE
DIAMOND
Identifying Minerals: Habit
Identifying Minerals: Form
Characteristic crystal shape; Related to crystallography
Characteristic form of crystals
Cubic
Laths
e.g. Pyrite
e.g. Feldspar
Sheets
Fibrous
e.g. Micas
e.g. Asbestos
Euhedral . . . . . . Subhedral . . . . . Anhedral
Quartz
Olivine
Quartz
Identifying Minerals: Cleavage
Planes of weakness within crystal lattice
Identifying Minerals: Hardness
Moh's
Scale of
Hardness
1. Talc
2. Gypsum
GYPSUM
3. Calcite
2.5 Fingernail
3.
Copper coin
4. Fluorite
5. Apatite
CALCITE
5.5 Pocket knife
6. Orthoclase
7. Quartz
8. Topaz
9. Corundum
QUARTZ
10. Diamond
Rocks
1. Igneous:
Frozen magma
2. Sedimentary:
Consolidated sediment grains
igneous & metamorphic rocks,
plant & animal material,
minerals precipitated from water
3. Metamorphic:
Igneous or sedimentary rocks
altered by heat and pressure
Rock Classification
1. Grain Size
2. Mineral Content
3. Texture
Generally applies to all 3 groups (ig, sed, met)
Igneous Rocks: Important Types
Minerals
Name
coarse
fine
Olivine, Pyroxene
Peridotite
Pyroxene, Feldspar
Gabbro
(Diorite
Granite
Mica, Quartz, Feldspar
Colour
Occurrence
Igneous Rocks: Grain Size
Grain Size depends on rate of crystal growth
Usually reflects depth of crystallisation: Intrusive vs Extrusive
Mantle
Basalt
Andesite)
Rhyolite
Dark
Light
Oceanic crust
Continental crust
Continental crust
Gabbro
Igneous Rocks:
Mantle
Peridotite
(Olivine +
Pyroxene)
Xenoliths
Basalt
Igneous Rocks: Composition
• Melting of mantle rocks
generates magma rich in
Mg & Fe ('Mafic') and poor
in SiO2
--> Gabbro & Basalt
OCEANS
• Re-melting and melting in
presence of water increases
SiO2 and decreases Mg, Fe
--> Granite & Rhyolite
CONTINENTS
Sedimentary Rocks
1. Clastic: Grains (clasts) of silicate minerals
Clastic Sed Rocks: Grainsize
Grainsize
{Clay
Silt
~0.01 mm
Sand
Pebbles
Cobbles
Boulders
Limestones
Evaporites
Cherts
Clastic Sed Rocks: Grainsize
few microns
Mud
2. Chemical
Rock Name
0.1–1 mm
~1cm
> 10cm
Claystone
Siltstone
Sandstone
} Mudstone
}
Conglomerate/
Breccia
Clastic Sed Rocks: Composition
Arenite:
Mainly quartz
Arkose:
Mainly Feldspar
Greywacke:Poorly sorted sand & mud
Breccia
Conglomerate
Lithic clast: Piece of rock
Metamorphic Rocks
Regional Metamorphism
• Protolith (original rock type)
• Type and degree of metamorphism
Regional (mountain building – temperature and pressure)
Contact (heat from igneous rocks)
Slate
slatey cleavage
Schist
foliation
Gneiss
Metamorphoism:
Influence of
Protolith
Limestones -> Marble
Sandstones -> Quartzites
Mafic Igneous -> Serpentinite