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Minerals: How do we classify them?


  • Minerals are usually formed in layers
  • Shape of minerals can change from environmental factors such as erosion and weathering (you will learn more about these soon)
  • Shapes of crystals found in minerals are used to identify them

Color and Streak

  • Color is one of the most commonly used properties to identify minerals
  • However, color can change due to weathering (i.e. rusting of iron)
  • Breaking a sample of a mineral will help to reveal its true color
  • The easiest way to do this is by way of a streak test, in which a sample of the mineral is scraped over a white, unglazed tile called a streak plate.
  • The colour of the powder mark that is left on the tile is usually a good clue to the mineral's identity.


  • Minerals vary a great deal in hardness, but scientists are able to determine ranges of hardness by way of a list called Moh's Scale.
  • The scale ranges from the softest mineral (talc) to the very hardest (diamond).
  • If two minerals are scratched across each other, the one that leaves a streak will always be the softest of the two.


  • Luster describes how a mineral or object reflects light.
  • It can also be described as glassy, waxy, oily, shiny and metallic.

Cleavage and Fracture

  • If a mineral can be split or broken on a flat plane then it has cleavage.
  • Minerals can split in one or many directions
  • If a mineral doesn't split on flat planes or shatters easily than it is said to have fracture.


Pennsylvania Geology | Which Way is North? | Geologic Explorations | Dino Inquiry | Wonderful World of Rocks and Minerals

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