Gypsum

Gypsum isvery soft mineral composedhydrous calcium sulfate, withformula CaSO₄·2H₂O. The anhydrous formcalled anhydrite.

image:desert-rose-small.jpg

desert rose, 10 cm long Larger version

Tablecontents

1 Occurrence 2 Details 3 Industrial uses 4 External link

Occurrence

It occurs as flattenedoften twinned crystalstransparent cleavable masses called selenite,may also occur silkyfibrous,which case itcommonly called satin spar; finallymay also be granular or quite compact. In hand-sized samples,can be anywhere from transparentopaque. A very fine-grained white or lightly tinted varietygypsumcalled alabasteris prizedornamental workvarious sorts. In arid areas, gypsum can occur inflower-like form often called desert rose.

Gypsum isvery common mineral,thickextensive beds associationsedimentary rocks. The largest deposits known occurstrata fromPermian age. Gypsumdepositedlakesea water, as well as hot springsfrom volcanic vapors,sulfate solutionsveins.

The word gypsumderived fromGreek meaning 'to cook',reference toburnt or calcined mineral. Becausegypsum fromquarries ofMontmartre districtParis hasfurnished burnt gypsum usedvarious purposes this material has been called plasterParis.

Details

Crystallographic system	Monoclinic
Colours	Colourlesswhitegrey thoughmay be tinted red, yellow, blue, brown, etc. by impurities.
Lustre	Vitreoussilky or pearly lustre
Hardness	1.5–2
Refractive index	1.522( average)
Specific gravity	2.31–2.33
Cleavage	2 good (66°114°)
Twinning	Very common
Pleochroism	Colourless

Industrial uses

• Blackboard chalk
• Sheetrock or wallboard,construction material
• Dental modes
• Surgical casts
• Paint filler
• Toothpaste
• Gesso

See also: Listminerals

External link

• WebMineral data

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Gypsumalsoplace name inStateOhio inUnited StatesAmerica. See Gypsum, Ohio.