Calcite Layered Mineral Specimen Fragment. A raw fragment of calcite with quartz and crystal layers with striations of color, notably a delicate pale green across the midsection. 

Size: 10 1/2 x 2 x 9 1/2 in. 

#4409 . 

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite is categorized with a mineral hardness level of 3 on the Mohs scale, 4 levels lower than quartz, with which it is sometimes confused due to similarities in crystalline structures. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses. Calcite is derived from the German Calcit, a term from the 19th Century that came from the Latin word for lime, calx. It has a vitreous luster, and the color is most frequently white or nearly transparent, though shades of gray, red, orange, yellow, green, blue, violet, brown, or even black can occur when the mineral is charged with impurities. They are often sought by collectors for this reason, as their translucent sheen takes colors so well that a virtual rainbow can be created within a single layer. There is a unique thermoluminescence property that was uncovered in the 20th Century during scientific experimentation that has made them also highly sought by companies using them for specific purposes, particularly in the optical, mechanical, and computer industries.