Formula: Ca(SO4).2H2O
Hydrated normal sulphate


Selenite is a transparent variety of gypsum
Desert rose is the name given to a (more or less) rose-like crystal group formed by precipitation in (usually) arid desert regions containing trapped sand particles. Usually, gypsum is the host mineral, but baryte, celestine and other minerals can form Desert Rose groups, too (Mindat).

Crystal System: Monoclinic
Specific gravity: 2.312 to 2.322 measured, 2.308 calculated
Hardness: 1½ to 2
Streak: White
Colour: Colourless, white, yellowish, pink
Solubility: Moderately soluble in hydrochloric acid

Evaporite deposits
Cave deposits

Gypsum is the commonest of the sulphate minerals, found in chemical sedimentary environments, where it frequently occurs interstratified with limestone and shale. It is usually found as a layer underlying beds of rock salt, having been deposited there as one of the first minerals to crystallise on the evaporation of salt waters. It may recrystallise in veins forming satin spar. It is also common as a gangue mineral in metallic veins, at fumaroles, and in the oxidation zones of sulphide deposits. Gypsum is also found in volcanic regions, especially where limestone has been acted on by sulphur vapours.
Gypsum is associated with many different minerals, the more common being halite, anhydrite, dolomite, calcite, sulphur, pyrite and quartz.


At the Mount Kelly deposit, Gunpowder District, Queensland, Australia, the copper ores overlie primary zone mineralisation consisting of quartz - dolomite - sulphide veins hosted in siltstone and schist. Gypsum occurs as millimetre sized crystals associated with hematite (AJM 22.1.24).

At Lake Crosbie, Victoria, Australia, gypsum occurs associated with halite and glauberite in black mud under a salt crust which covers the lake (AJM 10.1.17-18).

At Daye county, Hubei, China, chabazite pseudomorphs after gypsum have been found (KL p266).
Gypsum from Daye County - Image

At an unspecified locality in China, a blue desert rose has been found. It may be dyed blue, or it may be coloured by azurite. I bought it from a small mineral stall in a Shenzhen shopping centre (AESS).
Gypsum Desert Rose from China - Image

The Cave of Crystals, Naica Mine, Naica, Saucillo Municipality, Chihuahua, Mexico, is world-famous for giant gypsum crystals up to 14 m long. The cave is connected to the Naica mine at 300 m level, with almost unbearable conditions of 58oC and 90 to 99 percent humidity (Wiki).

At the Black Rock mine, Kuruman, South Africa, sturmanite pseudomorphs after gypsum have been found (KL p195).

At the Bristol Mineral Company's pits, Swan Inn, Yate, Gloucestershire, England, UK, gypsum has been found with minor celestine (RES p165).

At the Cliffs, Radcliffe on Trent, Nottinghamshire, England, UK, at an outcrop on the south bank of the river Trent, pseudomorphs of gypsum after halite to 3 cm occur (RES p 245).

At Gunthorpe Weir, East Bridgford, Nottinghamshire, England, UK, pseudomorphs of gypsum after halite occur (RES p248).
Gypsum at Gunthorpe Weir - Image

At Shotover Hill, Oxford, Oxfordshire, England, UK, many fine crystals of selenite have been found in clay, and this occurrence has been known since the late seventeenth century (RES p251).
Gypsum from Shotover Hill - Image

At the Magma mine, Pioneer District, Pinal county, Arizona, USA, gypsum is associated with baryte (R&M 95.1.85-86).

At Camp Verde, Yavapai county, Arizona, USA, fine replacement pseudomorphs of gypsum after glauberite have been found (R&M 94.2.163, KL p190).
Gypsum from Camp Verde - Image

In Nebraska, USA, quartz pseudomorphs after gypsum have been found (KL p249).
Gypsum from Nebraska - Image

At the Mid-Continent mine, Picher, Oklahoma, USA, a gypsum pseudomorph after calcite with melanterite on sphalerite has been found (KL p189).
Gypsum from the Mid-Continent Mine - Image

At the SK Star #2 Mining Claim, The Cove, Topaz Mountain, Thomas Range, Juab County, Utah, USA, specimens of the “rams horn” habit of gypsum have been found in the fault zone. Colourless with a pearly luster, these occur singly and in groups. The rams horns average under 3 cm (MinRec 51.6.809-810).
Gypsum from the SK Star #2 Mining Claim - Image


Glauberite dissolves in water, depositing gypsum, so pseudomorphs of gypsum after glauberite are not uncommon (AJM 10.1.17-18).

anhydrite and water to gypsum
Ca(SO4) + 2H2O ⇌ Ca(SO4).2H2O
Gypsum is frequently formed by the hydration of anhydrite.

anorthite, H2SO4 and H2 to gypsum and kaolinite
CaAl2 Si2O8 + H2SO4 + 3H2O → CaSO4.2H2O + Al2Si2O5(OH)4 (DHZ 5B p65)

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