Minerals
Solid/Crystalline
Elements or Compounds
Rock Forming Minerals
What are
minerals?
• Quartz
• Mica
• Feldspar
• Garnet
• Calcite
What types of
minerals are there?
Ore Minerals
Naturally Occurring
• Haematite
Crystallisation
from a Melt
• Quartz
• Micas
Gangue
• Galena
MINERALS
•Calcite
•Quartz
How are minerals formed?
Solution
(Evaporation)
• Halite
• Feldspars
Metamorphism
(solid state)
• Garnet
• Calcite
Crystallisation from
Hydrothermal Fluids in
Veins and Faults
• Gangue
• Ores
• Quartz
• Haematite
• Calcite
• Galena
• Gypsum
• Calcite
Crystallisation as a
cement from flowing
pore waters
• Quartz
• Calcite
How can minerals be identified?
•
Hardness
Moh’s Scale – fingernail, copper coin, steel nail
• Streak
Powder left on a porcelain tile (colour)
• Cleavage/fracture
Planes of weakness easily broken
• Density/ hefting
How heavy it is (by volume)
• Lustre
The way a mineral reflects light.
Vitreous/Metallic/Glassy/Dull/Transparent/Translu
cent
• Colour
Beware – some can show a range of colours
• Acid
HCl will fizz in the presence of CaCO3 (calcite)
Minerals
• Mineral 1 – black colour, hardness 2.5, one good
cleavage plane
Mica
• Mineral 2 – grey colour, scratches streak plate, no
cleavage
Quartz
• Mineral 3 – white in colour, hardness 6, 2 good cleavage
planes in some crystals Feldspar
• Mineral 4 – dark green/black in colour, hardness 5-6,
2 good cleavage planes at 90o
Augite
• Mineral 5 – white in colour, splits along 3 planes
Halite or Calcite
Minerals
Mineral 4
Mineral 2
Pink colour, hardness
6, 2 cleavage planes,
vitreous.
Black colour,
scratched by finger
nail, 1 cleavage
planes.
Mineral 1
White colour, hardness 6, 2
cleavage planes, vitreous.
Mineral 3
Colourless, scratches streak
plate, no cleavage planes,
vitreous.
Minerals are Formed by:
Crystallisation from a melt
Crystalline
interlocking texture
so rarely euhedral
Major minerals – quartz, feldspar, mica
Minerals are Formed by:
Metamorphic Recrystallisation
Crystalline
interlocking texture
often with overgrowths
Major minerals – calcite, garnet
Minerals are Formed by:
Evaporation
Crystalline
usually euhedral
Major minerals – halite
Minerals are Formed by:
Crystallisation as cement
from flowing pore waters
Crystalline
very fine grained
holds clasts together
Major minerals – quartz, calcite
Minerals are Formed by:
Crystallisation from
hydrothermal fluids
Crystalline
in veins and faults
crystallises out from
supersaturated fluids when cools
Major minerals – gangue, quartz,
calcite, ores: haematite, galena