Ask-a-Geologist #14: What are the properties of the mineral calcite?

Sophia asked: what are the properties of calcite? I’m especially interested in its cleavage directions and fracture pattern.

Calcite is a common mineral but has some unique properties. Calcite is very common and you can find it in most geologic setting around the world. It is the main component of limestone and marble. Calcite will dissolve in an acid which is why many caves form in massive limestone terraines when the mineral dissolves due to acid rain. Here are a few calcite fun facts:

  • Made of calcium carbonate,
  • Many colors; white, purple, yellow, red, orange, blue, green, brown and clear,
  • Very soft, a 3 on Mohs Hardness Scale,
  • Luster: Vitreous (Glassy) to Pearly,
  • Streak: White,
  • Specific Gravity: 2.71 g/cm3,
  • Cleavage: Three (3) directions of perfect cleavage means that it will break smoothly along cleavage planes, and forms a rhombohedral shape,
  • Fracture: Conchoidal

Not all samples of calcite that you will have that perfect rhombus shape. In the video I show you three samples of calcite. One of the samples is not a perfect rhombus but gives you hints of the cleavage.

Iceland spar calcite is a special version of clear quarterz. Its rhomb shape and clarity give it a unique optical property. When you put a sample of the Iceland Spar calcite over writing or an image it appears doubled through the mineral crystal.

I hope this gives you some fun information and a new appreciation for the mineral calcite. You can find out more about calcite on our website at


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