1. Natural dihydrous gypsum
Also known as gypsum, water gypsum or soft gypsum, a stable form of calcium sulfate in nature, chemical formula CaSO4·2H2O, chemical into CaO 32.6%, SO3 46.5%, H2O 20.9%. Generally white or colorless transparent, when containing impurities, gray brown, yellow and other colors.
2. Plaster of Paris
Main component CaSO4·H2O, white powdery solid. It is formed by dehydration of gypsum CaSO4·2H2O at 150℃. Gypsum of Paris is mixed with water to form a paste which gradually hardens and expands, and can be used to make plaster figures, models, chalk and medical plaster bandages.
3. Fiber plaster
It is a fibrous crystalline pure dihydrate gypsum aggregate, also known as fiber paste.
4. Transparent plaster
It is also a kind of pure dihydrous gypsum, gypsum forms a huge colorless or slightly reddish glassy transparent or translucent crystal, also known as through gypsum.
5. Alabaster
It is a coarse-crystal, dihydrous gypsum aggregate, countless crystal faces white flash to form a snowflake appearance, its purity is very high, also known as crystalline gypsum.
6. Ordinary plaster
A compact mass of fine-grained dihydrite gypsum, sometimes containing anhydrite, pale gray in color, often containing a certain amount of earth minerals and carbonate minerals. Most deposits are dominated by this kind of ore.
7. Argillaceous gypsum
It is a soft dihydrous gypsum ore containing more clay mineral impurities, referred to as mud paste.
8. Alpha hemihydrous gypsum
When dihydrous gypsum is dehydrated under pressurized water vapor or by heating in a solution of acids and salts, α-type hemihydrous gypsum is formed. α-type hemihydrous gypsum is well crystallized and solid, also known as high strength gypsum.
9. Beta hemihydrous gypsum
If the dehydration process of dihydrous gypsum is carried out in a dry environment without water vapor, the β-type semi-hydrous gypsum is formed. β-type hemihydrous gypsum is a flake and cracked crystal, the crystallization is very fine, the specific surface area is much larger than α-type hemihydrous gypsum, is the main component of building gypsum.
10. Anhydrite
Another stable form of calcium sulfate in nature, the chemical formula is CaSO4, chemical CaO 41.2%, SO3 58.8%. Pure anhydrite is clear, colorless, or white, gray because of impurities, and sometimes reddish or blue because of different minerals.
11. Anhydrite III
There are also two types of α-type and β-type gypsum, which are heated and dehydrated from α-type and β-type semi-hydrous gypsum, respectively. If the water vapor pressure is too low when the dihydrous gypsum is dehydrated, the dihydrous gypsum will directly change into β-type anhydrite III without passing through the semi-hydrous gypsum. Anhydrite III is unstable and highly hydrophilic, and can be converted into semi-aqueous gypsum even in slightly humid air.
12. Anhydrite II
It is dihydrous gypsum, semi-hydrous gypsum, anhydrous gypsum III by high temperature forging sintering, is insoluble or insoluble gypsum. It is a stable phase at room temperature and is often called superburnt gypsum.
13. Anhydrite I
It can only exist when the temperature is higher than 1180℃, otherwise it will be transformed into anhydrite II. Therefore, anhydrite I does not exist at room temperature.
