The origin of gypsum and Reserves
 The world's largest producer of gypsum in the United States.  In the United States, gypsum deposits in 22 states, a total of 69 mines, China's largest producing state in the Aida Fort Dodge.  Followed by Canada.  France in Europe a leading position in the production of gypsum.  Again for West Germany, Britain, West dental.

 China gypsum mine rich in resources.  23 provinces (regions) of the mineral gypsum.  The mine has proven reserves of 169 total 57.6 billion tons of ore reserves to maintain.  From the regional distribution, most gypsum mine in Shandong, accounting for 65% of reserves; Inner Mongolia, Qinghai, Hunan second.  Etuoke Banner of Inner Mongolia mainly gypsum mine, should the city of Hubei, Jilin, Hun River, Nanjing, Jiangsu, Shandong Dawenkou, Qinzhou, Taiyuan, Shanxi, Ningxia Zhongwei gypsum mine and so on.  Sedimentary gypsum deposits to dominated the country's total reserves of more than 90%, epigenetic and hydrothermal metasomatic type gypsum mine is not very important.  Gypsum mine in the geological age of both outputs to Early Cretaceous and Tertiary sedimentary gypsum is the most important.

 The structure and form of gypsum
 Monoclinic, a0 = 0.568nm, b0 = 1.518nm, c0 = 0.629nm, β = 118 ° 23 '; Z = 4.  Crystal structure consists of [SO4] 2 - tetrahedral linked with Ca2 + into % (010) double, double rooms connected by H2O molecules.  The complete cleavage that occurs along this direction.  Ca2 + coordination number is 8, and the adjacent 4 [SO4] tetrahedra in the six O2-and two H2O molecules link.  H2O molecules and [SO4] in the O2-linked by hydrogen bonds between water molecules linked to the molecular bond.

 Oblique Fang Zhujing class, C2h-2 / m (L2PC).  Often by the crystal growth plates, also grainy.  Often a simple form: parallel-sided b, p, orthorhombic column m, l, etc.; crystal surface and often with vertical stripes; sometimes were lenticular.  Twinning common, one is by (100) double-crystal surface, said Gary dovetail twins or twins, the other is (101) as twin plane or bus, said Li Shuangjing arrow twins.  Mostly dense granular or fibrous aggregates.  Fine grain-like blocks called alabaster; fibrous aggregates called fiber gypsum.  Rare crystals formed by the lenticular-shaped rose-like aggregates.  Also earthy, flaky aggregates.

 Physical and chemical properties of gypsum
 Usually white, colorless, colorless, transparent crystal called through the plaster, sometimes due to impurities and ash, light yellow, light brown and other colors.  Streak white.  Transparent.  Glass, luster, cleavage plane pearl luster, shiny silk fibrous aggregates.  Cleavage very full, and the medium, the angle between cleavage plane broke into 66 pieces and 114 of the diamond shape.  Brittle.  Hardness of 1.5-2.  Slight change in different directions.  The relative density of 2.3.

 Polarizing microscope: colorless.  Biaxial crystal (+).  2V = 58.  Ng = 1.530, Nm = 1.523, Np = 1.521.  2V decreases with increasing temperature, at about 90 , 2V zero.

 Discharge of heated water of crystallization there are 3 stages: 105 ~ 180 , the first discharge of a water molecule, and then immediately discharged half of the water molecules, into a burning gypsum Ca [SO4] • 0.5H2O, also known as gypsum plaster or semi-water .  200 ~ 220 , discharge the remaining half of the water molecules into b anhydrite Ca [SO4] • ε H2O (0.06 <ε <0.11).  About 350 , type a into gypsum Ca [SO4].  1120 , further into type ` anhydrite.  Melting temperature of 1450 .

 Microporous structure of gypsum dehydration and heat to make a good sound and heat insulation and fire performance.

 Occurrence and the combination of gypsum
 Main products of the chemical deposition, often forming a huge ledge or lens, occurs in limestone, red shale and sandstone, marl and clay rocks, often with the anhydrite, rock salt and other symbiotic.  Anhydrite layers in the near-surface area, due to the decrease of outside pressure, by the action of surface water into gypsum: CaSO4 +2 H2O - CaSO4 • 2H2O; while volume increased about 30% of the damage caused by gypsum layer.

 Industrial application of gypsum
 Gypsum is monoclinic, a high degree of cleavage, easily split into thin sheets.  The gypsum is heated to 100-200 ° C, lose some crystallization water, gypsum hemihydrate can be obtained.  It is a hard cementitious material gas, with α and β are two forms were tested diamond crystal, but different physical properties.  crystallization of α-hemihydrate gypsum good, solid; β-type Hemihydrate is flaky and cracked crystals, crystal is very small, specific surface area than the α-hemihydrate gypsum is much greater.

 When the production of gypsum products, α-type hemihydrate gypsum need less water than β-type, products, higher density and strength.  Often used in saturated steam autoclave steam condensed media is made of α-hemihydrate gypsum, also known as gypsum; open the device with a wok or a rotary kiln is made of calcined β-mixing half water, gypsum, which is building gypsum.  Industrial by-products of chemical gypsum plaster the same properties with natural, without too much processing.  Semi-water slurry mixing gypsum and water re-formation of dihydrate gypsum, condensation in the drying process quickly gained strength hardening, but the water is softened.

 Cementitious materials is the production of gypsum plaster and gypsum building products, the main raw material is Portland cement retarder.  The 600-800 ° C calcined gypsum, add a small amount of lime, pulverized catalyst together, we can get anhydrite binder (also known as Guinness Book Binder); by 900-1000 ° C calcined and pulverized, calcined gypsum can be hot .  Obtained by the two gypsum products, stronger than gypsum products, and anhydrite binder has good insulation, high temperature calcined gypsum has good abrasion resistance and water resistance.

 Use of gypsum building products produced are:

 ` plaster board.  Adding a small amount of gypsum in building adhesives, fiber, foam agent after mixing with water pouring in a row between two layers of tissue paper protection, and then by rolling, freezing, cutting, drying made.  Thickness 9-25 mm, dry bulk density 750-850 kg / m 3, plate toughness, non-combustible, dimensionally stable, smooth surface, can be sawn, to facilitate construction.  Mainly used for the walls, veneer walls, ceilings, acoustic panels, but the water is poor, should not be used in humid environments.

 a fiber gypsum board.  Will be mixed with fibers and other additives in the gypsum slurry, with the wound, filter press or other method of roll forming, by cutting, freezing, drying made.  Thickness of 8-12 mm, compared with plaster board, and its high flexural strength, tissue paper and adhesives do not care, but the bulk density greater use of the same with plaster board.

 b decorative gypsum board.  The preparation of the gypsum slurry, at the end of die casting mold box with a pattern, the smooth, coagulation, stripping, drying is made, the thickness of 10 mm.  In order to improve its sound absorption effects, can also be made with a perforated and blind holes of the plate, commonly used for ceilings and wall decorations.

 c hollow gypsum lath and plaster block.  Casting the gypsum slurry into the mold, shape and solidified by the vibration of stripping, drying made.  The thickness of the hollow of the plate is 60-100 mm, 30-40% porosity; block size is generally 600 × 600 mm, thickness of 60-100 mm, surrounded by high population, and sometimes can be made hollow with a hole block.  Hollow of the plate and the blocks are cast with a special masonry, construction convenient, commonly used for non-load bearing interior partition wall.