Chemistry · Ch 5 — Alkali and Alkaline Earth Metals
Gypsum (CaSO4.2H2O)
Gypsum (CaSO4.2H2O)
Gypsum beds formed as water evaporated from massive prehistoric sea basins (Figure 5.11): as the water evaporated, the dissolved minerals became concentrated and crystallised out.
Properties. Gypsum is a soft mineral, moderately soluble in water, and this solubility is affected by temperature in an unusual way: unlike most salts, gypsum becomes less soluble as the temperature rises -- a distinguishing characteristic called retrograde solubility.
Gypsum is usually white, colourless or grey, though impurities can give it shades of pink, yellow, brown or light green. Its crystals sometimes form in a shape resembling flower petals, a habit called a "desert rose," typically found in arid or desert regions.
Gypsum has low thermal conductivity, which is why it is used in drywalls/wallboards -- it also serves as a natural insulator. Alabaster, a granular, opaque variety of gypsum, is highly valued as an ornamental stone and has been used by sculptors for centuries (Figure 5.12). Gypsum has a hardness of 1.5-2 on Mohs' hardness scale and a specific gravity of 2.3-2.4. …
What this figure shows. A landscape photograph of an open gypsum quarry, showing pale, layered mineral beds exposed by mining, illustrating that gypsum occurs in large thick beds near the earth' …
What this figure shows. A photograph of a carved/polished alabaster object -- a granular, opaque, fine-grained variety of gypsum long prized as an ornamental and sculptural stone. …
What this figure shows. A collage of small photographs illustrating gypsum's varied uses -- drywall/plasterboard sheets, a bag or block of plaster of Paris, an agricultural field being conditioned with gypsum, and toothpaste/personal-care products -- summarising the range of applicati …