GYPSUM
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.