Gypsum is a moderately common hydrous calcium sulfate mineral (CaSO4·2H2O).  Gypsum has a nonmetallic luster, is usually clearish to whitish, is soft (H≡2), and rather fragile/brittle.  Gypsum has 3 cleavage planes, one of which is well developed (“one good cleavage), and the other two are not well developed (“two poor cleavages”).  Broken gypsum specimens are frequently thin plates - the consequence of the one good cleavage plane.


Gypsum has economic value as a mineral.  It is the starting ingredient for making plaster and wallboard.


Gypsum (specimen on left measures 2.7 cm across along top) - cleavage fragments (above & below) with the three different cleavage planes labeled:

"1" represents the large front & back "good cleavage" surfaces (facing the viewer); "2" and "3" represent the "poor cleavage" surfaces developed along the edges.




Gypsum - nice unbroken gypsum crystal (3.9 cm across) showing monoclinic symmetry from Willow Creek near Nanton, Alberta, Canada.



Gypsum - cluster of radiating gypsum blades from Whyalla Norrie, South Australia.



Gypsum - large crystals of gypsum like this are often referred to by the name selenite.  Selenite is widely considered a “variety” of gypsum.  It is not.  It is gypsum.  It does not differ in any way from gypsum.  “Gypsum” is the only proper name, and “selenite” should not be used.  (CMC RM 1288, Cincinnati Museum Center's rock & mineral collection, Cincinnati, Ohio, USA)



Gypsum - "selenite roses" (left: 2.2 cm across; right: 2.3 cm across).  These subspheroidal masses of complexly intersecting gypsum crystals form in some desert settings.



Gypsum - "fishtail selenite" from the Naica Mine, Chihuahua State, Mexico.



Gypsum from Naica, Chihuahua State, Mexico.



Gypsum from the Bou Becker Mine, Touissit, Morocco.



Gypsum from the Bou Becker Mine, Touissit, Morocco.



Gypsum from Santa Eulalia, Chihuahua State, Mexico.



Photo gallery of gypsum



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