Ca[SO 4 ]·2H 2 O [Chemical composition] There are often mechanical inclusions such as clay and organic matter. [Crystal structure] monoclinic system; Figure H-18 Crystal and twin crystal of gypsum (quoted from Pan Zhaoyu et al., 1993) (a) (b) (c) single crystal, (d) (e) (f) twin; parallel double sided: b {010}, p {103}; slanted square: m {110}, l {111} Figure H-19 Plate crystal of gypsum [Form] Crystals often develop into plate-like shape according to {010}, and some are granular (Fig. H-18, H-19); crystal faces {110} and {010} often have vertical stripes. Common twin crystals, one is a double crystal or a dovetail twin crystal according to (100) as a double crystal plane (Fig. H-18(d), (e)), and the other is a double crystal plane with (101) Paris double crystal or arrow double crystal (see Figure H-18(f)). The aggregates are mostly dense or fibrous. The fine-grained block is called alabaster; the fibrous aggregate is called fiber gypsum. Rose-like aggregates formed by lentil crystals are less common. In addition, there are soil-like and sheet-like aggregates. [Physical properties] usually white and colorless, colorless transparent crystal called transparent gypsum, sometimes dyed with other impurities Gray, light yellow, light brown, etc.; streaks white; transparent; glass luster, cleavage surface is pearl luster, fibrous aggregate is silky luster. The cleavage {010} is extremely complete, {100} and {011} are medium, and the cleavage sheet is split into a rhombohedron with an angle of 66° and 114°, and the cleavage sheet is flexible. The hardness is 1.5 to 2, and the direction is slightly changed. The relative density is 2.3. Crisp. [genesis and occurrence] is mainly a product of chemical deposition. It often forms a huge ore layer or lens body existing between limestone red shale and sandstone , marl and clay rock, and is symbiotic with anhydrite and stone salt. In the oxidized zone of the sulfide ore deposit, the primary sulfide is oxidized to form sulfuric acid, and then the surrounding rock of the limestone can form gypsum. Hydrothermally occurring gypsum is less common and is commonly found in low temperature hydrothermal sulphide deposits. [Identification characteristics] Low hardness, with a set of extremely complete cleavage and various characteristics of the shape can be identified. The gypsum formed into a dense block can be distinguished from the carbonate mineral by its low hardness and no acidity. [Main use] It is widely used for the production of cement, plaster and its products, such as sculpture, architectural decoration and fireproof materials. HVOF Powder,Chromium Carbide Powder,Chromium Carbide Coating,Chromium Carbide Thermal Spray Powder Luoyang Golden Egret Geotools Co., Ltd , https://www.hvofpowders.com
a 0 = 0.568 nm, b 0 = 1.518 nm, c 0 = 0.629 nm; β = 113 ° 50'; Z = 4. Since Ca 2+  is small, H 2 O is introduced when combined with [SO 4 ] 2- . The crystal structure of gypsum is characterized by: [SO 4 ] 2- tetrahedron and Ca 2+ are connected to a double layer parallel to (010), and the two layers are connected by H2O molecules, and the complete cleavage of gypsum occurs in this direction. The coordination number of Ca 2+ is 8, which is linked to 6 O 2 - and 2 H 2 O molecules in the adjacent 4 [SO 4 ] 2- .
Gypsum
Plaster (Gypsum), also known as gypsum or gypsum.