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.
| 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 |
Black 
White 
Colorless 
Yellow 
Brown 
Blue 
Pink 
Gray Alabaster, Desert Rose, Gypsite, Satin Spar, Selenite
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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.
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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.
| Common Name | Alabaster |
| Specific Gravity | 2.250 |
| Toughness | Poor |
| Stability | Poor |
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.
| 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 |
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.
| Common Name | Desert Rose |
| Toughness | Poor |
| Stability | Poor |
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.
| Common Name | Selenite |
| Specific Gravity | 2.250 |
| Stability | Poor |
This page was created on June 27, 2014.
This page was last edited on October 24, 2019.
