Gypsum

Object/Artifact

-

Crater Rock Museum

Name/Title

Gypsum

Entry/Object ID

2009.62.8

Description

Chemical Composition: PbS Crystal System: Monoclinic System Description: Common Name: Gypsum Chemistry: CaSO4-2(H2O), Hydrated Calcium Sulfate Group: Sulfates Location: Mexico Description: Light brown, looks sandy, looks like a rose 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. Best Field Indicators are crystal habit, flexible crystals, cleavage and hardness. Fracture: uneven Hardness: 2 Gypsum Luster: Vitreous Occurrence: Gypsum is a common mineral, with thick and extensive evaporite beds in association with sedimentary rocks. Deposits are known to occur in strata from as early as the Permian age.[5] Gypsum is deposited in lake and sea water, as well as in hot springs, from volcanic vapors, and sulfate solutions in veins. Hydrothermal anhydrite in veins is commonly hydrated to gypsum by groundwater in near surface exposures. It is often associated with the minerals halite and sulfur Rock Type: Sedimentary Specific Gravity: 2.3 Streak: white Texture: Microcrystaline 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 Collection

Acquisition

Accession

2009.62

Source or Donor

Museum Collection of Minerals

Acquisition Method

Donation

Dimensions

Width

2-1/2 in

Depth

1/2 in

Length

4-1/2 in

Weight

0.37 oz

Dimension Notes

Dimension taken at widest points

Location

Location

Shelf

CS-G-7

Room

Curation Storage

Building

Crater Rock Museum

Category

Permanent