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How to Tell the Difference Between Talc & Gypsum

Rocks and minerals all have different characteristics, including hardness and luster. The Mohs Hardness Scale is the primary scale that tests a rock's hardness by how easily it can be scratched. Diamond has a score of 10 on the hardness scale, which is the highest a mineral can obtain. Talc has a score of 1, and gypsum has a score of 2, which makes these two minerals similar and difficult to differentiate between.

Instructions

- 1
  Feel both pieces of rock for how slippery they are. If the rock is slippery, it may be talc. If the rock isn't slippery it may be gypsum.
- 2
  Fragment pieces of each rock with your fingernail. If cleavage fragments fall off and are tiny, the specimen is talc. Cleavage on talc is perfect. Cleavage is the quality of a split along defined planes of a rock or mineral. In this case, you would be splitting the rock with your fingernail.
- 3
  Scratch each piece of rock. If powder falls off and doesn't feel slippery or greasy, it's gypsum.
- 4
  Check the colors of each. Talc will have a gray, white, green or silver color to it. It can also have a dull, pearly or greasy luster. Gypsum can be colorless, white and gray with yellow, red and brown shades to it. Gypsum can also have a pearly luster to it.

Rocks & Minerals