Sedimentary rockforming Minerals

1
Sedimentary rock-forming Minerals

• The specification states
• that you need to be able to describe the
  physical characteristics and origin of the major
  sedimentary rock-forming minerals and the
  identification of
• Quartz
• Potash Feldspar
• Muscovite
• Calcite
• Gypsum
• Halite
• Haematite

2
Quartz

• Composition SiO2
• Crystals hexagonal in cross section
• Hardness 7
• Density 2.7
• Colour usually white or colourless
• Lustre vitreous
• Streak white
• Cleavage none
• Fracture conchoidal

3
Potash Feldspar

• Composition KAlSi3O8
• Crystals roughly rectangular
• Hardness 6 6.5
• Density 2.6
• Colour pink, white or grey
• Lustre vitreous to pearly
• Streak white
• Cleavage 2 good
• Fracture conchoidal

4
Muscovite

• Composition KAl2(AlSi3)O10(OH)2
• Crystals hexagonal
• Hardness 2.5 - 3
• Density 2.8 2.9
• Colour colourless, white or silvery
• Lustre vitreous to pearly
• Streak white
• Cleavage 1 perfect
• Other Flexible

5
Calcite

• Composition CaCO3
• Crystals rhomb shaped
• Hardness 3
• Density 2.7
• Colour usually colourless or white
• Lustre vitreous
• Streak white
• Cleavage 3 perfect
• Fracture conchoidal (rare)
• Other reacts with dilute HCl

6
Gypsum

• Composition CaSO4.2H2O
• Crystals roughly rhomb shaped or fibrous
• Hardness 2
• Density 2.3
• Colour colourless or white
• Lustre vitreous or pearly. Silky
• Streak white
• Cleavage 1 perfect
• Fracture conchoidal

7
Halite

• Composition NaCl
• Crystals cubic (ideally)
• Hardness 2.5
• Density 2.2
• Colour usually colourless or white
• Lustre vitreous
• Streak white
• Cleavage 3 perfect
• Fracture conchoidal
• Other soluble and tastes of salt. Feels greasy.

8
Haemetite

• Composition Fe2O3
• Crystals botryoidal
• Hardness 6
• Density 5
• Colour black or red-brown
• Lustre metallic
• Streak red-brown
• Cleavage none
• Fracture uneven