Drywall: Made from Gypsum
Gypsum, or calcium sulfate dihydrate (CaSO₄·2H₂O), constitutes the main component of drywall. Gypsum is also used in fertilizer, as a paint extender, and to make plaster of Paris.
Occurrence
Gypsum, an "evaporite" mineral from water-soluble sediments, deposits through the evaporation of surface water. Sand particles and other inclusions make up part of the resultant mineral.
Structural Forms
Its most beautifully occurring form may be the "Desert Rose," but gypsum occurs in a number of other forms, including "selenite." Selenite is Greek for "moon" and gives off a moon-like glow. Other forms of gypsum include alabaster and satin spar--a fibrous form that transmits light up and down its fibers.
Crystals
Officially, gypsum forms monoclinic 2/m prismatic crystals, and some gypsum crystals rate among the largest in the world.
Unit Cell
Gypsum can be classified as soft, semi-vitreous, pearly, silky, and dull. Some minerals seem cool to the touch--they conduct heat away from the fingers; however, since gypsum makes an excellent insulator, its crystals feel warm to the touch. The smallest possible gypsum crystal defines a "unit cell." The three unit cell axes, a, b, and c, are not all perpendicular. The b and c axes are perpendicular, as are axes a and b; however, axes a and c are not. Angle β = 118.43º.
Atomic Structure
Loyola University provides a visual Java applet of gypsum's space group and bonding on its website (see References).
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