Gypsum Value, Price, and Jewelry Information
Gypsum is one of the most abundant minerals, but gem-quality crystals are very rare. This material is extremely difficult to facet but very easy to carve into sculptures and decorative objects.
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|Varieties||Alabaster, Satin Spar, Selenite|
|Alternate Common Names||Varieties: alabaster, satin spar, selenite.|
|Crystallography||Monoclinic. Crystals often perfect and large; tabular; rosettes; lenticular; helictites are grotesque shapes found in caves; often twinned; massive; granular.|
|Colors||Colorless, white, gray, black; impurities make it yellowish, reddish, brownish, greenish, pink, bluish, orangish. Sometimes banded and patterned like marble.|
|Luster||Subvitreous; pearly on cleavages.|
|Polish Luster||Waxy to subvitreous.|
|Fracture Luster||Dull to pearly.|
|Hardness||1.5 to 2, varies with direction.|
|Specific Gravity||2.32 (range 2.30-2.33)|
|Cleavage||Perfect and easy, 1 direction; distinct 2 other directions|
|Luminescence||May show fluorescence and sometimes phosphorescence. Can show a wide range of colors in SW and LW, the most commonly encountered are bluish, orange-yellow, yellow, greenish, and brownish. Selenite crystals often exhibit zoned "hourglass" fluorescence that may, or may not, be evident in ordinary light. Inert in X-rays.|
|Enhancements||Dyeing, common. Bleaching, common. Coating. Occasional heating to improve color, prepare for dying.|
|Transparency||Transparent to Opaque|
|Absorption Spectrum||Not diagnostic.|
|Optics||a = 1.520; β = 1.523; γ = 1.530. Biaxial (+), 2V= 58°.|
|Etymology||Gypsum from the Greek gypsos, a name applied to what we now call plaster. Satin spar in allusion to the satiny luster of the fibrous material. Selenite from the Greek selene for “moon,” due to the pearly luster on cleavage surfaces. Alabaster from the Greek alabastros, a stone used to make ointment vases.|
|Occurrence||In sedimentary rocks and deposits; saline lakes; oxidized parts of ore deposits; volcanic deposits.|
Gypsum’s physical properties make it extremely challenging to facet. It has perfect and easy cleavage in three directions and, depending on its orientation, a tenacity that can make it either bendable or breakable. It’s both water soluble and very heat sensitive. Gypsum also famously represents the hardness of 2 on the Mohs scale, which means it’s very easy to scratch. (In some directions, gypsum may actually have an even lower hardness of 1.5).
For these same reasons, gypsums would make unlikely choices for jewelry use. In addition, they usually show no attractive colors, though impurities may add pale shades. This material has a surprisingly high dispersion of 0.033 but just can’t receive a cut to show it off. Of course, a faceted piece would make a rare addition to a mineral or gem collection. Crystals can occur in very unusual natural shapes and may also show astonishing “water-like” transparency.
Artisans have used this massive, granular variety of gypsum for thousands of years to make objects such as bowls, vases, and sculptures. Alabaster is very easy to carve and is used today for ashtrays, clock housings, paperweights, and so forth. Carved alabaster objects still have a very low softness. However, scratches on these can be polished out rather more easily than on small stones. (Please note: the term “alabaster” sometimes refers to a form of opalescent glass, likely due to its appearance. Glass and gypsum, however, have very distinct properties).
This massive, fibrous variety of gypsum can be carved or cabbed. Brown satin spar can make lovely decorative items. Some satin spar cabochons may show very pronounced chatoyancy or a “cat’s eye” effect. The noted mineralogist and folklorist George F. Kunz wrote that egg-shaped satin spar cabs from Egypt were sometimes called “Pharaoh’s Eggs” and were purported to be lucky, just like satin spar cabs from Niagara Falls — supposedly recovered from gypsum deposits beneath the waterfalls at great peril. (These tourist stones were sometimes called “Niagara spar”).
Colorless, transparent gypsum crystals are called selenite. Those rare, faceted gypsums would most likely be considered selenites.
Gypsum crystals may form in curved shapes that resemble the horns of a ram.
In desert regions, minerals such as barite and gypsum can occur as tabular crystals with rose-like shapes. (The crystals form the petals of the rose, so to speak). These stones contain trapped sand particles.
Some gypsums, but not all, may luminesce, showing both fluorescence and phosphorescence. They may show a wide range of colors in shortwave (SW) and longwave (LW) ultraviolet light (UV). The most commonly encountered include the following: bluish, orange-yellow, yellow, greenish, and brownish. Gypsums are inert in X-rays.
A twinned selenite crystal growing from a ball of selenite crystals. These selenites fluoresce bluish green in UV light and also phosphoresce. 3.2 x 2.0 x 1.8 cm, Block and Brady One Pit, Red River Floodway, near, Winnipeg, Manitoba, Canada. © Rob Lavinsky, www.iRocks.com. Used with permission.
Selenite crystals often exhibit zoned “hourglass” fluorescence that may, or may not, be evident in ordinary light.
Both calcite and gypsum are abundant but rarely faceted minerals. As transparent crystals and faceted gems, they may look very similar, especially when colorless. (Calcites have a wider and richer range of colors). Although calcite has a higher hardness (3) than gypsum, a scratch test may not be the best way to test a potentially rare faceted specimen. A specific gravity (SG) test can easily distinguish these gems. Calcite has a higher SG range (2.71-2.94) than gypsum (2.30-2.33).
Gypsum has a myriad practical uses and a long history of industrial applications. Despite its abundance, gypsum is also widely synthesized — as an industrial by-product — for many purposes. However, there’s no known jewelry use for this synthetic material.
Of course, gypsum’s physical properties make it an unlikely choice for synthetic jewelry material. However, gypsums may be encountered as simulants or imitations of other more valuable or well-known gemstones. For example, gypsum has been used in the manufacture of assembled cabochons designed to imitate rainbow moonstones.
Gypsum can take dyes and coatings very easily.
The most common sulfate mineral, gypsum has many sources all over the world. It occurs especially in evaporite environments.
One of the most celebrated occurrences, the “Cave of the Crystals” in Naica, Chihuahua, Mexico contains gigantic selenite crystals. The largest found so far measures 39’ x 13’ and weighs 55 tons.
Other gem-quality sources include the following:
- United States: Arizona; California (many locations); Colorado; Kansas; Michigan; New Mexico; New York; South Dakota; Utah; other states.
- Australia; Canada; Braden, Chile (crystals reported up to 10’ long); China; Czech Republic; Egypt; Germany; Peru; Russia; Spain.
Notable sources of alabaster include Tuscany, Italy and England, United Kingdom.
Lapidaries could cut cabochons and carvings of almost size desired from massive gypsum. Fibrous material could yield large carvings up to several pounds. Faceted selenites could reach hundreds of carats, since large transparent crystals do exist. (Only the fragile nature of the material limits the finished size).
Gypsums are best reserved for display in a gem or mineral collection. Jewelry use isn’t recommended.
Never use mechanical systems, which use heat or vibrations, to clean any gypsum pieces. Since the material can be quite porous, clean by hand and only with warm water with no detergents. Pat dry carefully; don’t rub or scrub the piece.
For more care recommendations, consult our gemstone jewelry cleaning guide.