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Gypsum (plaster)
HYDRATED CALCIUM SULPHATE
Chemistry
Chemistry available on new site, see link above
Miscellaneous
- Family: Other
- Region: None
- Mined At: Unspecified
- Raw Mineral: No
- Generic: No
Notes
Specific Gravity: 2.3
Hardness: 3
Plaster (gypsum, alabaster) is calcium sulphate CaSO4 2H2O. It is the crystalline mineral from which plaster is made. Gypsum has three different decomposition cycles, depending on temperature. At 120-200C and 500C water is liberated, at 1000-1100C it decomposes completely.
Plaster is not practical as a source of CaO in glazes because its decomposition produces large amounts of sulpfur trioxide which is dangerous to health.
Plaster reacts with sodium silicate and soda ash in a calcium-for-sodium ion exchange, and this process will eventually clog the pore structure of a mold. The use of polyacrylate deflocculants will prevent this (and have other advantages).
Data
- Specific Gravity: 1200.00
- Specific Gravity: 1200.00
Suppliers
- Generic
Authors
- Tony Hansen (Owner)
XML
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