COMMON ROCK-FORMING MINERALS

Mineral Definition: naturally-occurring, inorganic solid with an ordered atomic arrangement and well-defined chemical composition

Simplified Classification of Mineral Lab Samples
LUSTER/COLOR
CLEAVAGE Metallic Non-Metallic/Dark Non-Metallic/Light
4 DirectionsFluoriteFluorite
3 Directions at 90oGalenaHalite
3 Directions at75oand 105oCalcite
2 Directions at 90oCa-Plagioclase/PyroxeneK-Feldspar/Na-Plagioclase
2 Directions at 56oand 124oAmphibole
1 DirectionBiotiteMuscovite
No CleavageHematite/PyriteHematite/Limonite/Quartz/OlivineQuartz/Olivine

PART I - Non-Silicate Minerals

GALENA

  • Chemical Formula: PbS (lead sulfide)
  • Mineral Group: sulfides
  • Luster/Color: metallic/silver-gray
  • Cleavage: 3-directions at 90o
  • Hardness: 2.5
  • Other Characteristics: high specific gravity (7.6), gray streak, mined for lead (lead ore)

    • PYRITE

  • Chemical Formula: FeS2 (iron sulfide)
  • Mineral Group: sulfides
  • Luster/Color: metallic/gold or brassy-yellow
  • Cleavage: absent
  • Hardness: 6 to 6.5
  • Other Characteristics: common cubic crystals, high specific gravity (5)

    • HEMATITE

  • Chemical Formula: Fe2O3 (iron oxide)
  • Mineral Group: oxides
  • Luster/Color: non-metallic (sometimes metallic)/red-brown
  • Cleavage: absent
  • Hardness: 6.0
  • Other Characteristics: red-brown streak, high specific gravity (5), commonly associated with limonite, granular or massive aggregates

    • LIMONITE

  • Chemical Formula: Fe2O3.H2O (hydrated iron oxide)
  • Mineral Group: oxides
  • Luster/Color: non-metallic/yellow brown
  • Cleavage: absent
  • Hardness: 5 to 5.5
  • Other Characteristics: yellow-brown streak, moderate to high sepcific gravity (3.5-4), commonly associated with hematite, massive or fibrous aggregates

    • CALCITE

  • Chemical Formula: CaCO3 (calcium carbonate)
  • Mineral Group: carbonate
  • Luster/Color: non-metallic, often glassy/usually colorless or white, otherwise variable
  • Cleavage: 3 directions at 75o and 105o
  • Hardness: 3
  • Other Characteristics: reacts to weak HCL acid

    • HALITE

  • Chemical Formula: NaCl (sodium chloride)
  • Mineral Group: halides
  • Luster/Color: non-metallic/mostly colorless
  • Cleavage: 3 directions at 90o
  • Hardness: 2 to 2.5
  • Other Characteristics: salty taste, high solubility

    • FLUORITE

  • Chemical Formula: CaF2 (calcium fluoride)
  • Mineral Group: halides
  • Luster/Color: non-metallic, often glassy/variable
  • Cleavage: 4 directions
  • Hardness: 4
  • Other Characteristics: cubic crystals, dipyramidal cleavage fragments

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