Physical Properties of Minerals

• Colour


  Determined by the chemical composition of the mineral

  Not a good diagnostic property.
• Lustre


  The way in which a mineral reflects light

  Controlled by the atomic structure
• Vitreous Lustre


  Glass-like

  Transparent, Translucent or Opague
• Metallic Lustre


  Reflect light by metal
• Pearly Lustre


  Mother of pear like -> rainbow colours shown when catching the light
• Silky Lustre


  Silk-like; occurs in minerals with a fiborous structure
• Dull Lustre


  Doesn’t reflect light
• Adamantite Lustre


  Lustre of a diamond
• Streak


  Colour of a minerals powder

  Obtained by rubbing on white porcelain tile

  Useful for identifying metallic ore minerals

  Any minerals harder than 6 will scratch the tile
• Hardness

  Measure of Mohs Scale - from 1 -> 10

  Steel Nail = 5.5

  Copper Coin = 3.5

  Fingernail = 2.5
• Cleavage


  The way a mineral breaks

  Controlled by lines of weakness

  Can have 1,2,3 or 4 planes of cleavage

  Can be perfect,good or poor
• Fracture


  Way a mineral breaks when struck by a hammer

  Bonds between atoms are strong so no cleavage

  Not controlled by weakness in the atomic structure
• Conchoidal Fracture

  The same as that shown by window glass

  Diagnostic Feature = Quartz
• Acid Reaction


  Use dilute HCL to test for carbonates - Calcite givers of CO2
• Taste


  Halite tastes salty -> Diagnostic Property
• Form/Habit


  Common appearance of the mineral

  Only noted if it helps identify

  Acicular = Needle-like crystals

  Tabular = Thin cuboid-like crystals

  Bladed = Like tabular but comes to a point
• Diagnostic Properties


  Properties that allow any minerals to be identified

  Most minerals have at least 1

  Hardness, Cleavage & Streak are most useful

  Colour and Lustre are least useful
• Specific Gravity or Relative Density


  Ratio of density of a mineral compared to the density of an equal volume of water