Name/Title
GypsumEntry/Object ID
2015.1.27Description
Chemical Composition: CaSO4*2H2O
Crystal System: Monoclinic System
Description: Common Name; Gypsum Rose
Chemistry; CaSO4*2H2O
Class: Sulfates
Location; Chihuahua, Mexico
Description: A cluster of bladed gypsum formed in mounds and" Roses". Color is a light purplish tan.
PHYSICAL CHARACTERISTICS:
Color is usually white, colorless or gray, but can also be shades of red, brown and yellow.
Luster is vitreous to pearly especially on cleavage surfaces.
Transparency crystals are transparent to translucent.
Crystal System is monoclinic; 2/m
Crystal Habits include the tabular, bladed or blocky crystals with a slanted parallelogram outline. The pinacoid faces dominate with jutting prism faces on the edges of the tabular crystals. Long thin crystals show bends and some specimens bend into spirals called "Ram's Horn Selenite" Two types of twinning are common and one produces a "spear head twin" or "swallowtail twin" while the other type produces a "fishtail twin". Also massive, crusty, granular, earthy and fiberous.
Cleavage is good in one direction and distinct in two others..
Fracture is uneven but rarely seen.
Hardness is 2 and can be scratched by a fingernail.
Specific Gravity is approximately 2.3+ (light)
Streak is white.
Best Field Indicators are crystal habit, flexible crystals, cleavage and hardness.
Fracture: Uneven
Hardness: 2 Gypsum
Luster: Vitreous
Occurrence: Notable Occurances include Naica, Mexico; Sicily; Utah and Colorado, USA; and many other locallities throughout the world.
Rock Type: Sedimentary
Specific Gravity: 2..4
Streak: White
Variety: Gypsum has several variety names that are widely used in the mineral trade.
"Selenite" is the colorless and transparent variety that shows a pearl like luster and has been described as having a moon like glow. The word selenite comes from the greek for Moon and means moon rock.
Another variety is a compact fiberous aggregate called "satin spar" . This variety has a very satin like look that gives a play of light up and down the fiberous crystals.
A fine grained massive material is called "alabaster" and is an ornamental stone used in fine carvings for centuries, even eons.Collection
RAGM Mineral CollectionOther Names and Numbers
Other Number
Other Number: 78.63.135Dimensions
Width
9-1/2 inDepth
7 inLength
14 inLocation
Location
Shelf
DS-10-ARoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
ExhibitMoved By
Jillian Mather KettleyDate
June 4, 2025Notes
Moved from ds-10-B and location addedLocation
Shelf
Bottom-cubby, Bottom-cubbyRoom
Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Rawley WyattDate
July 9, 2015