Calcite Mineral

AKA: CaCO₃.
Context:
- It can have a trigonal crystal system and can occur in various crystal habits including scalenohedra, rhombohedra, and prisms.
- It can (typically) have a Mohs hardness of 3, which makes it relatively soft and easily scratched by a metal blade.
- It can range from being transparent to opaque.
- It can exhibit various colors depending on the presence of impurities.
- It can have a high birefringence, and when a clear calcite crystal is placed over an image or text, it will create a double image, a property known as double refraction.
- It can reacts with acid, causing it to effervesce.
- It can be an abundant mineral found in a wide variety of geologic settings, from sedimentary rocks like limestone, which is composed primarily of calcite, to metamorphic rocks, and in hydrothermal veins.
- It can be a common constituent of fossil shells and stalactites and stalagmites in caves.
- It can be used in the production of cement, as a flux in steelmaking, in agricultural soil treatment, and more.
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Example(s):
- in Iceland Spar is a clear variety of calcite that is well known for its optical properties, including double refraction.
- in Marble is a metamorphic rock composed primarily of calcite.
See: Carbonate Mineral, Limestone, Marble, Calcium Carbonate, Crystal System, Mohs Hardness, Birefringence, Acid, Fossil, Stalactite, Stalagmite, Vaterite, Peridotite, Polymorphism (Materials Science).

References

(Wikipedia, 2021) ⇒ https://en.wikipedia.org/wiki/Calcite Retrieved:2021-8-14.
- Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO₃). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite". Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite is even less stable.