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Physical and optical properties of minerals

Short answer

Physical properties include colour, streak, hardness on Mohs scale, cleavage (e.g., mica one, calcite three), fracture (conchoidal in quartz), specific gravity, and crystal habit. Optical properties are lustre (metallic, vitreous, pearly), transparency, double refraction (calcite), and effects like fluorescence and pleochroism.

Describe the physical and optical properties of minerals (in hand specimen).

Minerals in hand specimen are identified by their physical properties, many of which relate to the way they interact with light (optical properties).

Physical properties

  • Colour: general appearance; may vary with impurities (quartz).
  • Streak: colour of powder on unglazed porcelain; more constant than colour.
  • Hardness: resistance to scratching on the Mohs scale (1 to 10).
  • Cleavage: splitting along smooth planes (mica one, feldspar two, calcite three directions).
  • Fracture: irregular breakage without cleavage (conchoidal in quartz).
  • Tenacity: brittle, malleable, flexible, elastic.
  • Specific gravity: relative density (quartz 2.65, galena 7.5), tested by heft.
  • Habit/form: shape of crystal aggregates (prismatic, fibrous, granular).
  • Others: magnetism, taste, feel, effervescence with HCl.

Optical properties

  • Lustre: metallic (galena), vitreous (quartz), pearly (talc), silky (asbestos), resinous, greasy, earthy, adamantine.
  • Transparency: transparent (clear quartz), translucent (milky quartz), opaque (pyrite).
  • Colour and play of colour: opalescence, iridescence, asterism.
  • Refraction and double refraction: calcite shows two images of an object seen through it.
  • Fluorescence and phosphorescence: glow under ultraviolet light (fluorite).
  • Pleochroism: change of colour with viewing direction (seen under the microscope).

✓ Answer checked by Claude Opus 5.5 (high effort)

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