Gypsum too, especially in clay.
Gypsum is a soft
sulfate mineral composed of
calcium sulfate dihydrate, with the
chemical formula CaSO
4·2H2O.
[3] It is widely mined and is used as a
fertilizer and as the main constituent in many forms of
plaster,
blackboard/
sidewalk chalk, and
drywall. A
massive fine-grained white or lightly tinted variety of gypsum, called
alabaster, has been used for
sculpture by many cultures including
Ancient Egypt,
Mesopotamia,
Ancient Rome, the
Byzantine Empire, and the
Nottingham alabasters of
Medieval England. Gypsum also crystallizes as translucent crystals of
selenite. It forms as an
evaporite mineral and as a
hydration product of
anhydrite.