Calcite Composition

Calcite contains 56.03% CaO and 43.97% CO2, often Mn and Fe, sometimes Sr. Its name comes from the fact that it is easy to break into square blocks along its cleavage. In Compendium of Materia Medica, Li Shizhen holds that calcite "resembles anhydrite blocks, which are cracked into square blocks and whose walls are bright, is also known as calcite".


Calcite can often see good crystals, common crystals are hexagonal column {1010} and rhombohedral {0112} polygon, compound trigonal partial triangular {2131}, rhombohedral {0112}, etc., rhombohedral {1011} single crystal (as cleavage block shape) is relatively rare; according to (0112) into a common sheet of twin crystals, the result of stress; also shows {0001} contact twin. The aggregates are granular, dense and massive, bell-like, tubercular, oolitic, bean-like, soil-like (chalky) and so on.


The color of calcite varies with the impurities contained in it, such as yellowish, reddish, brown and black when containing iron and manganese, but generally white or colorless. Colorless and transparent calcite is also called Icelandic stone (named for its abundance in Iceland). It has a wonderful feature that it can see double images of objects. Therefore, Icelandic stone is an important optical material. Calcite is the main mineral of limestone and marble. It has many uses in production and life. We know that limestone can form karst caves. The stalactites and stalagmites in the caves are actually composed of calcite.


On August 17, 2004, Xu's jewelry studio in Guiyang City, Guizhou Province, donated two of the world's largest calcite gemstones to the collection of the China Geological Museum. One of the gems (right) is a light yellow, inverted Portuguese cut calcite gem weighing 172.5 carats; the other (left) is a golden brown, close hexagonal calcite gem weighing 84 carats. Both gems weigh more than 75.8 carats of golden-brown stepped polished calcite stones collected at the Smithsonian Museum in the United States. These two calcite gemstones have been elaborated by Xu's jewelry studio in Guiyang City for more than two years from 2000 to 2002, which fills in the blank of Chinese brilliant calcite gemstone processing.


It often contains isomorphic substitutes such as Mn, Fe, Zn, Mg, Pb, Sr, Ba, Co, TR, etc. When they reach a certain amount, they can form manganese calcite, iron calcite, zinc calcite, magnesia calcite and other varieties. In addition, brucite, dolomite, hydroxides of iron and mechanical mixtures of oxides, sulfides and quartz are also common in crystals.