Minerals

MINERALS

What are minerals? What types of

minerals are there?

How are minerals formed?

Solid/Crystalline Elements or Compounds

Naturally Occurring

Rock Forming Minerals

Ore Minerals

• Haematite

• Galena

Crystallisation from a Melt

Solution (Evaporation)

• Halite

• Gypsum

• Calcite

• Quartz

• Micas

• Feldspars

• Quartz

• Feldspar

• Mica

• Garnet

• Calcite

Metamorphism (solid state)

• Garnet

• Calcite

Crystallisation as a cement from flowing

pore waters• Quartz

• Calcite

Crystallisation from Hydrothermal Fluids in Veins and Faults

• Gangue

• Quartz

• Calcite

• Ores

• Haematite

• Galena

Gangue•Calcite•Quartz

How can minerals be identified?

• Hardness

• Streak

• Cleavage/fracture

• Density/ hefting

• Lustre

• Colour

• Acid

Moh’s Scale – fingernail, copper coin, steel nail

Powder left on a porcelain tile (colour)

Planes of weakness easily broken

How heavy it is (by volume)

The way a mineral reflects light. Vitreous/Metallic/Glassy/Dull/Transparent/Translucent

Beware – some can show a range of colours

HCl will fizz in the presence of CaCO3 (calcite)

Minerals

• Mineral 1 – black colour, hardness 2.5, one good cleavage plane

• Mineral 2 – grey colour, scratches streak plate, no cleavage

• Mineral 3 – white in colour, hardness 6, 2 good cleavage planes in some crystals

• Mineral 4 – dark green/black in colour, hardness 5-6, 2 good cleavage planes at 90o

• Mineral 5 – white in colour, splits along 3 planes

Mica

Quartz

Feldspar

Augite

Halite or Calcite

Minerals

Mineral 1

White colour, hardness 6, 2 cleavage planes, vitreous.

Mineral 2

Pink colour, hardness 6, 2 cleavage planes, vitreous.

Mineral 3Colourless, scratches streak plate, no cleavage planes, vitreous.

Mineral 4

Black colour, scratched by finger nail, 1 cleavage planes.

Minerals are Formed by:

Crystallisation from a melt

Crystalline interlocking textureso rarely euhedral

Major minerals – quartz, feldspar, mica

Minerals are Formed by:

Metamorphic Recrystallisation

Crystallineinterlocking texture

often with overgrowths

Major minerals – calcite, garnet

Minerals are Formed by:

Evaporation

Crystallineusually euhedral

Major minerals – halite

Minerals are Formed by:

Crystallisation as cementfrom flowing pore waters

Crystallinevery fine grained

holds clasts together

Major minerals – quartz, calcite

Minerals are Formed by:

Crystallisation from hydrothermal fluids

Crystallinein veins and faults

crystallises out from supersaturated fluids when

coolsMajor minerals – gangue, quartz, calcite, ores: haematite, galena