Calcite is one of the most common and widespread minerals. It is a principal component of most sedimentary carbonate rocks (limestone, chalk, travertine, etc.) but occurs in metamorphic (marble, hydrothermal veins) and igneous rocks (carbonatite) also.
It (CaCO3) usually forms anhedral (without well-developed crystal faces) grains in limestone and marble. In marble, crystals are usually larger, but some limestones (grainstones) may be pretty coarse as well and are therefore sometimes erroneously called marble as well (mostly for marketing purposes). Calcite is also a cementing mineral in clastic sediments and an important biomineral. Microorganisms with calcareous tests usually prefer aragonite (chemically also calcium carbonate), but as time goes by these aragonitic shells recrystallize to calcite.
It may form as a direct chemical precipitate (travertine) or as a gangue mineral in veins, but most of it is somehow connected to life. The mineralization may be directly biologically controlled (growth of shells), but also biologically induced (blooms of drifting marine microorganisms that induce the crystallization of calcite crystals on their surface), which results in whitish tropical water and contributes to the growth of carbonate banks.
Calcite in metamorphic rocks is sometimes associated with calc-silicate minerals. These are silicate minerals that contain lots of calcium and are the products of chemical reactions between carbonate rocks and hot silicate (magmatic) liquids. Such rocks are called skarns.
Calcite is not a common mineral in igneous rocks, but it may occur in alkali-rich (high Na- and K-content) rocks containing feldspathoids like nepheline or sodalite. Carbonatite is a rare and still somewhat mysterious igneous rock that is usually composed mostly of calcite.
It is an important industrial mineral with many uses. It is a principal raw material in cement industry. Intense heating will drive off carbon dioxide and produce quicklime (CaO). Quicklime and hydrated lime can be used in many ways: as a mortar, flux in metallurgy, filler in paper, soil stabilization, sugar refining, wastewater treatment, and in dietary supplement pills because calcium is a major macromineral (note that the term “mineral” has a different meaning here, chemical element calcium is no mineral in a geological sense because it is highly reactive and therefore does not occur alone).
I could easily mistake the last example with a serpentine marble.
Yes, similar colors. I should have a photo of serpentine marble somewhere also but not yet prepared to be published. I collected this carbonatite sample in Finland (Siilinjärvi mine) few years ago.
Offtopic – humor-site people have also discovered sand under microscope: http://www.cracked.com/article_19953_9-normal-things-that-look-trippy-under-microscope.html 😀
A nickname for some sand found in Florida is “sugar sand”. It is characterized by small grainsize, minimal aggregation, very low compaction, and poor capture of organic material. What is the proper technical name for this type of sand, and what (if anything) can be done to improve its compaction and ability to hold organic material?
Hola que tal, tengo una duda sobre un tipo de roca con pequeños cristales incrustados me parece que son de Calcuta pero no se que nombre tiene realmente
I got nearly 5kls rocks not too sure what it is. But pretty sure it’s a calcite. I wonder if someone can check it I’m just not too sure what types of rock is it.