Name/Title
SeleniteEntry/Object ID
78.63.140Description
Chemical Composition: CaSO4-2(H2O),
Crystal System: Monoclinic System
Description: Minerals
Museum location: Case # 42
Common Name: Gypsum
Group Name: Sulfates
Location: White Sands, New Mexico
Chemistry: CaSO4-2(H2O),
Descriptionh: Delmar described this specimen as a striking piece of transparents, clear selenite gypsum. One large crystal stick up out of a mass of crystals and is quite spectacular, though broken and reglued. It is still loose however.
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.
Associated Minerals are halite, calcite, sulfur, pyrite, borax and many others.
Other Characteristics: thin crystals are flexible but not elastic, meaning they can be bent but will not bend back on their own. Also some samples are fluorescent. Gypsum has a very low thermal conductivity (hence it's use in drywall as an insulating filler). A crystal of Gypsum will feel noticeably warmer than a like crystal of quartz.
Notable Occurances include Naica, Mexico; Sicily; Utah and Colorado, USA; and many other locallities throughout the world.
Best Field Indicators are crystal habit, flexible crystals, cleavage and hardness.
Fracture: uneven
Hardness: 2 Gypsum
Luster: Vitreous
Occurrence: "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
Specific Gravity: 2.3
Streak: white
Variety: Gypsum is a very soft mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O
Gypsum occurs in nature as flattened and often twinned crystals and transparent cleavable masses called selenite. It may also occur silky and fibrous, in which case it is commonly called satin spar. Finally it may also be granular or quite compact.Collection
Delmar Smith Mineral CollectionAcquisition
Accession
78.63Source or Donor
Delmar Smith Crystal CollectionAcquisition Method
DonationDimensions
Height
4-3/16 inWidth
5-1/2 inLength
3 inDimension Notes
Dimension taken at widest pointsLocation
Location
Shelf
cubby, cubbyWall
northRoom
Wood room, Delmar Smith HallBuilding
Crater Rock MuseumCategory
PermanentMoved By
Catherine BoydDate
December 26, 2008Location
Shelf
cubbyCabinet
case #42Wall
northRoom
Wood room, Delmar Smith HallBuilding
Crater Rock MuseumCategory
Permanent