[Chemical composition] The chemical composition is relatively stable, Si is sometimes replaced by Al, and Mg can be replaced by Fe, Mn, Ni, and Al.
[Crystal structure] TOT type, three octahedral type. Multi-type phenomenon has yet to be studied, and it is more likely to use 2M 1 type. 
a 0 = 0.527 nm, b 0 = 0.912 nm, c 0 = 1.855 nm; β = 100 °; Z = 4.
[Form] The fine crystals are pseudo hexagonal or rhomboid plate-like flakes, but they are rare and often densely packed (Fig. G-43).
Figure G-43 Crystal aggregate of talc
[Physical properties] Pure is white, with other light colors when it contains impurities; glass luster, cleavage surface reveals pearl luster. The cleavage {001} is extremely complete; the dense block is a shell-like fracture. Hardness 1. The relative density is 2.58 to 2.83. It has a smooth feel and good smoothness. The cleavage sheet is flexible.
Causes of occurrence and [] Talc is a typical hydrothermal minerals, magnesium-rich substance ultrabasic rocks, dolomite, dolomitic limestone,
A product that has been metabolized by hydrothermal deterioration. Such as:
Mg 2 [SiO 4 ]+2CO 2 +4H 2 O→Mg 6 [Si 4 O 10 ](OH) 8 +2MgCO 3
Peridot serpentine
Mg 6 [Si 4 O 10 ](OH) 8 +3CO 2 →Mg 3 [Si 4 O 10 ](OH) 2 +3MgCO 3 +3H 2 O
Serpentine talc magnesite
3CaMg[CO 3 ] 2 +4SiO 2 +H 2 O→Mg 3 [Si 4 O 10 ](OH) 2 +3CaCO 3 +3CO 2
Dolomite talc
China's Liaoning, Shandong and other places contain abundant talc resources, especially the talc produced in Liaoning, which is famous in the world for its excellent scale and quality.
[Identification features] Low hardness, slippery feel, and the sheet is extremely cleavable. Similar to pyrophyllite , the difference is
With the cobalt nitrate method, after the talc is burned, it reacts with cobalt nitrate to become rosy, while the pyrophyllite becomes blue. The acidity test is a simpler method. A drop of water is dripped on the bisque plate, and the emulsion is lightly ground for about half a minute to obtain a turbid aqueous solution. The litchi paper is qualitatively tested for its acidity and alkalinity. Alkaline (pH about 9), pyrophyllite is acidic (pH about 6).
[Main use] The electrical insulation and heat resistance of talc (refractory degree is 1490~1510 °C) is high. Resistant to strong acid and alkali. Its ultrafine powder has good adsorption (the talc powder absorption can reach 49%~51%) and the coverage (the coating prepared by talc powder can cover the object tightly and evenly). Therefore, it is widely used in ceramics, paper, paint, plastics, rubber, cosmetics and other industries. Block talc porcelain has good dielectric properties and mechanical strength, is a high-frequency electric porcelain insulation material; talc is also used for lubricants, magnesium Fertilizer and so on.
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