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  • Gypsum

Gypsum

Gypsum

By Tim Matthews, JD, FGA, GG, DGA,
CEO and President of JTV
Published: June 2014
Modified: January 2022
Gypsum Polished Gypsum Rough
Table of Contents
  • General Information
  • Gypsum Colors
  • Alternate Names
  • Countries of Origin
  • Care
  • Species/Variety

Gypsum is a mineral that has been utilized since antiquity. This soft mineral represents the second level on the Mohs hardness scale. Cut stones are rare because gypsum has perfect cleavage, and it is too soft to facet. The fine-grained variety known as alabaster is used for carvings and decorative objects. Selenite is the large crystalline variety that is popular with mineral collectors. The fibrous variety is known as satin spar. Gypsum sometimes crystallizes in rosette patterns known as desert roses. Gypsum is probably best known for its use in construction materials like sheetrock, cement, and plaster.

General Information

  • Classification
  • Optical Properties
  • Characteristic Physical Properties
  • Chemistry & Crystallography
Common Name
Gypsum
Species
Gypsum
Transparency
Opaque-Transparent
Dispersion
Strength: Strong Fire
Refractive Index
1.519-1.530
Birefringence
0.009- 0.010
Optic Character
Biaxial
Optic Sign
Positive
Polariscope Reaction
Aggregate (AGG), Doubly Refractive (DR)
Fluorescence
SWUV: Typically bluish white but can be yellowish green, green, bluish white, greenish white, pinkish white, yellowish white, white, pale yellow, yellow
LWUV: Typically yellowish white but can be green, greenish white, yellowish white, bluish white, pale yellow, orange yellow
Pleochroism
None
Hardness
1.5-2
Streak
White
Specific Gravity
2.200-2.400
Toughness
Poor
Luster
Vitreous, Dull, Waxy, Silky, Pearly
Fracture
Granular, splintery and conchoidal
Cleavage
Perfect
Chemical Name
Hydrated calcium sulfate
Chemical Formula
CaSO4.2H2O
Crystal System
Monoclinic
Chemistry Classification
Sulfate

Gypsum Colors

  • Black Gypsum
    Black
  • White Gypsum
    White
  • Colorless Gypsum
    Colorless
  • Yellow Gypsum
    Yellow
  • Brown Gypsum
    Brown
  • Blue Gypsum
    Blue
  • Pink Gypsum
    Pink
  • Gray Gypsum
    Gray

Alternate Names

Alabaster, Desert Rose, Gypsite, Satin Spar, Selenite

Countries of Origin

Niger (the); Papua New Guinea; Angola; Kazakhstan; Paraguay; Portugal; Moldova (the Republic of); Solomon Islands; Greece; Latvia; Mongolia; Morocco; Unknown; Panama; Chile; Argentina; Isle of Man; Ukraine; Zambia; India; Canada; Turkey; Belgium; Namibia; Finland; South Africa; Georgia; Peru; Turkmenistan; Venezuela (Bolivarian Republic of); Germany; Yemen; Tanzania, United Republic Of; United Arab Emirates (the); Eritrea; Fiji; Madagascar; Thailand; Kiribati; Libya; Costa Rica; Sweden; Liechtenstein; Russian Federation (the); Poland; Jordan; Tunisia; Palestine, State of; Croatia; Syrian Arab Republic; Tuvalu; Kenya; Switzerland; Spain; Djibouti; Lebanon; Azerbaijan; Cuba; Mauritania; Saint Lucia; Lao People's Democratic Republic (the); Australia; Tajikistan; Estonia; Myanmar; Cyprus; Malaysia; Iceland; Oman; Bosnia And Herzegovina; Armenia; Austria; Mozambique; Korea (the Republic of); Luxembourg; Brazil; Algeria; Slovenia; Colombia; Ecuador; United States of America (the); Hungary; Japan; Taiwan (Province of China); Albania; Bolivia (Plurinational State of); Trinidad And Tobago; New Zealand; Vanuatu; Senegal; Italy; Antarctica; Ethiopia; Afghanistan; Czechia; Egypt; Malta; Saudi Arabia; Pakistan; China; Ireland; Qatar; Sudan (the); Slovakia; France; Lithuania; Serbia; Bahamas (the); Kyrgyzstan; Bhutan; Romania; Dominican Republic (the); Uzbekistan; Netherlands (the); Barbados; Nicaragua; Norway; Botswana; Denmark; Mexico; Zimbabwe; Philippines (the); Greenland; Montenegro; Indonesia

Care

Due to its soft nature gypsum needs to be kept away from harder materials that will damage its surface. Gypsum will turn cloudy if exposed to heat.

Species/Variety

Alabaster

Alabaster is a fine-grained massive form of gypsum. Alabaster ranges from white to yellow, pink, and brown. Due to its porosity it is often dyed. It has been used for centuries for statues, carvings, and other ornamental purposes. Treated alabaster is used as a marble simulant. Due to its extreme softness, it is ideal for fashioning into works of art.

  • Classification
  • Characteristic Physical properties
Common Name
Alabaster
Specific Gravity
2.250
Toughness
Poor
Stability
Poor

Satin Spar

Satin spar is an adjective used when the fibrous habit of a mineral gives it a satin luster. The term satin spar has been used in the past to describe calcite and aragonite; however, it is currently accepted as one variety of the mineral gypsum, along with selenite and alabaster.

Satin Spar Gypsum
Satin Spar Gypsum
  • Classification
  • Optical Properties
  • Characteristic Physical properties
Common Name
Satin Spar
Refractive Index
1.52-1.529
Tolerance:(+0.001/-0.001)
Birefringence
0.009-0.01
Fluorescence
SWUV: Inert to weak brownish to greenish white
LWUV: Inert to weak brownish to greenish white
Specific Gravity
2.25
Inclusions
Satin spar is a white to cream fibrous gypsum with chatoyant effect.
Stability
Fair

Desert Rose

When gypsum forms in rose like patterns it is called a desert rose. They are found in desert regions where liquid containing gypsum evaporates leaving the gypsum to crystallize. Gypsum roses can be distinguished from barite roses by their sharp edges. Desert roses from Chihuahua, Mexico have distinctive white edges.

Desert Rose Gypsum
Desert Rose Gypsum
  • Classification
  • Characteristic Physical properties
Common Name
Desert Rose
Toughness
Poor
Stability
Poor

Selenite

Selenite is the name for transparent, colorless to near colorless crystals of gypsum, a hydrous calcium sulfate that is found in a number of forms. The name "selenite" comes from the Greek word selene, meaning "moon", no doubt in reference to the gem's white glow. Gypsum, in all varieties, is very soft and has perfect cleavage so it should be handled with care.

Selenite Gypsum
Selenite Gypsum
  • Classification
  • Characteristic Physical properties
Common Name
Selenite
Specific Gravity
2.250
Stability
Poor
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