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They're Minerals, Marie!

Cobaltoan Calcite

The word "mineral" may mean different things to different people - some may associate it with gemstones, with rocks and geology, or even vitamin pills.

To a geologist, however, a mineral is a naturally occurring, inorganic, solid element or compound with a definite composition and a regular internal crystal structure.

There are over 2000 known varieties of minerals. However, most of these are fairly rare, and are sought by mineral collectors for their gem quality. The more common minerals add up to about 200 or so varieties. The most important of the common minerals are silicates (compounds containing the elements silicon and oxygen, and usually a metallic element) and carbonates (carbonates containing carbon, oxygen, and a metallic element). The other common minerals may be collectively called non-silicates.

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Calcite is best recognized by its relatively low Mohs hardness (3) and its high reactivity with even weak acids, such as vinegar, plus its prominent rhombohedral cleavage in most varieties.

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