Calcite
Carbonate · CaCO₃
Calcite is calcium carbonate, a very common mineral that fizzes in acid, cleaves into rhombs and shows striking double refraction in clear crystals.
What is calcite?
Calcite is calcium carbonate and one of the most widespread minerals, the main component of limestone and marble. It comes in an enormous range of crystal shapes and colours, cleaves into slanted rhomb-shaped blocks, and clear “Iceland spar” crystals famously double any image seen through them.
Properties
- Chemical formula
- CaCO₃
- Category
- Carbonate
- Hardness (Mohs)
- 3
- Crystal system
- Trigonal
- Lustre
- Vitreous
- Streak
- White
- Colour
- Colourless, white, and every colour
- Cleavage / fracture
- Perfect rhombohedral (three directions)
How to identify calcite
- →Fizzes readily in dilute hydrochloric acid (even weak vinegar reacts slowly).
- →Perfect rhombohedral cleavage: breaks into slanted blocks.
- →Hardness 3: scratched by a copper coin or knife.
- →Clear crystals show strong double refraction.
Where calcite is found
Calcite is found worldwide. Superb crystals come from England, Mexico, the USA (Elmwood, Tennessee) and Iceland.
Calcite finds on minShelf
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