The chemical composition of calcite is CaO(56.03%) and CO2(43.97%), which usually contains Mn, Fe and sometimes Sr. Its name comes from the fact that calcite is easily broken into square fragments along cleavage. In Compendium of Materia Medica, Li Shizhen thinks that calcite is "like anhydrite, which can be solved by striking blocks. If the wall is bright, it is also called calcite. " Good crystals can often be seen in calcite. The common crystal forms are hexagonal columnar {10 10} and rhombic {0 12} aggregates, compound triangles {2 13 1} and rhombic {01}. Diamond {10 1 1} single crystals (such as cleavage blocks) are rare. According to (0 1 12), it is common to form twins, which is the result of stress. It is also shown as {000 1} contact twins. Aggregates are granular, dense, stalactite, nodular, oolitic, pea-shaped, earthy (chalky) and so on. The color of calcite varies with the impurities it contains. When it contains iron and manganese, it is light yellow, light red and brown-black, but it is generally white or colorless. Colorless calcite is also called Iceland spar (named for its abundance in Iceland). Such calcite has a wonderful feature, that is, it can see double images of objects. Therefore, Iceland spar is an important optical material. It is the main mineral of calcite, limestone and marble, and has many uses in production and life. We know that limestone can form caves, and stalactites, stalagmites and white marble in caves are actually made of calcite. Calcite On August 17, 2004, Xu Zhubao's studio in Guiyang, Guizhou Province successfully polished two of the world's largest calcite gems and donated them to the collection of geological museum, China. One of the gems (right) is a light yellow, Portuguese-style cut calcite gem, weighing 172.5 carats; The other (left) is a golden yellow-brown hexagonal calcite gem, weighing 84 carats. These two gems weigh more than the 75.8-carat gold-brown stepped-cut polished calcite gem in the Smithsonian Museum. These two calcite gems were carefully polished by Guiyang Xu Zhubao Studio from 2000 to 2002, which filled the blank of processing brilliant calcite gems in China. Isomorphic substitutes containing manganese, iron, zinc, magnesium, lead, strontium, barium, cobalt and thallium; When they reach a certain amount, manganese calcite, iron calcite, zinc calcite and magnesium calcite can be formed. In addition, mechanical mixtures such as brucite, dolomite, iron hydroxide, oxide, sulfide and synchrotron are also common in crystals. Genesis event editor