Gypsum

Object/Artifact

-

Crater Rock Museum

Name/Title

Gypsum

Entry/Object ID

2009.62.124

Description

Chemical Composition: Hydrated Calcium Sulfate Crystal System: Monoclinic System Description: Common Name: Gypsum Chemistry: CaSO4-2(H2O), Hydrated Calcium Sulfate Class: Sulfates Location: Weisssshan, Yunnan, China Description: Very large specimen with approximately six highly elongated transparent crystals extending from a multi-structured base including a druzy white crystalline structure mixed with a dull, white, cotton-ball like crystalline structure on a dull white and tan granular matrix. 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: 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

Collection

RAGM Mineral Collection

Acquisition

Accession

2009.62

Source or Donor

Museum Collection of Minerals

Acquisition Method

Donation

Dimensions

Width

9-1/2 in

Depth

7 in

Length

9-1/4 in

Weight

13.33 oz

Location

Location

* Untyped Location

RD-6

Category

Exhibit

Moved By

Jillian Mather Kettley

Date

August 21, 2025

Notes

Location added when performing inventory