3.41-ct anhydrite, medium light purplish-pink, freeform step cut, 15.4 x 5.6, Iran. © The Gem Trader. Used with permission.
Rare and difficult to cut, anhydrite is seldom faceted. However, this material can be carved into beautiful objects. “Angelite,” a blue-gray variety, has become a popular choice for cabochons.
| Data | Value |
|---|---|
| Name | Anhydrite (Angelite) |
| Colors | Colorless, white-gray, pale blue, blue-gray, violet, pinkish, rose, reddish, brownish. |
| Crystallography | Orthorhombic. Crystals equant, thick, tabular or (rarely) prismatic; massive, cleavable. |
| Refractive Index | 1.570-1.614 |
| Luster | Greasy; pearly on cleavage; vitreous in massive varieties. |
| Hardness | 3-3.5 |
| Fracture | Uneven to splintery |
| Specific Gravity | 2.9-2.98 |
| Birefringence | 0.044 |
| Cleavage | Perfect 1 direction, nearly perfect 1 direction |
| Dispersion | 0.013 |
| Luminescence | Red color in LW UV (Germany) |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long |
| Transparency | Translucent to transparent. |
| Absorption Spectrum | Not diagnostic |
| Formula |
CaSO4 |
| Pleochroism |
In violet crystals: colorless-pale yellow/pale violet-rose/violet. |
| Optics |
α = 1.570; β = 1.575 γ= 1.614. Biaxial (+), 2V ~ 43°. |
| Optic Sign | Biaxial + |
| Etymology |
From the Greek anhydros for “waterless,” in allusion to its composition. |
| Occurrence |
A rock-forming mineral, associated with gypsum beds, halite, and limestones. Also occurs in hydrothermal veins, cavities in basalts, and other traprocks. |
| Inclusions |
Multiphase cavities; crystal minerals. |
Discovered around 1900, this beautiful violet anhydrite crystal rests on a feldspar matrix with another paler anhydrite emerging from it. 2.6 x 2.0 x 1.9 cm. Simplon Railway Tunnel, Valais, Switzerland. © Rob Lavinsky, www.iRocks.com. Used with permission.
Anhydrite doesn’t occur in abundance. When exposed to water over time, it alters into the much more commonly found gypsum. Not surprisingly, facetable material is rarer still. Furthermore, with excellent cleavage planes in three directions, anhydrites prove challenging to cut and fragile for wear. With a hardness range of 3-3.5, they’re very susceptible to scratching, which further limits their use as jewelry stones.
Nevertheless, historically, artisans and jewelry makers have carved objects and cut cabochons from this material.
Anhydrites usually have pale, soft colors. Blues, violets, and pinks are especially prized.
Anhydrite, 4.9 x 3.1 x 2.1 cm, Niccioleta Mine, Massa Marittima, Grosseto Province, Tuscany, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.
This translucent, blue-gray anhydrite variety known by the trade name “angelite” or “angeline” has become a popular gem material. Discovered in Peru, it was introduced to worldwide gem markets in the late 1980s. This material has been used for beads, spheres, and carvings. Of course, these trade names carry deliberate angelic connotations. The gem’s color may evoke sky blue or, perhaps, a “heavenly” blue.
“Bct139_yannaelle,” angelite and bronze-colored metal bracelet, by Imaginarium-Annelise. Licensed under CC By 2.0.
This white-gray, marble-like textured material comes from Volpino, Italy. It’s used locally for cabs and as a decorative stone.
Anhydrite that occurs in folded, concretionary forms is known as bowel stone. This variety name also carries deliberate connotations.
“Slithering biogeochemical sediments slip slidin’ away,” a “seriously folded slice” of anhydrite from Crownest Pass, Rocky Mountains, Alberta, Canada. Photo by Mike Beauregard. Licensed under CC By 2.0.
The Ancient Egyptians used white anhydrite as well as a distinctive blue-tinted variety to create beautiful objects. However, the ancient source of the blue material, which takes a good polish, has never been found.
Kohl Pot, ca. 1938-1700 BCE. Anhydrite, 1¾” diameter x 1⅝” height. (4.5 x 4.1 cm). Brooklyn Museum, Charles Edwin Wilbour Fund, 07.447.206. Licensed under CC By 3.0.
Because of the intersection of anhydrite’s cleavage planes at right angles, these gems may break apart and reveal cube-like (pseudo-cubic) forms. This appearance has led to another name for this gemstone: “cube spar.” Despite appearances, anhydrites have an orthorhombic crystal habit, not a cubic or isometric habit.
Note the cube-like formations in this fractured piece of anhydrite. Gypsum Quarry Arnave, Tarascon-sur-Ariège, Ariège, Midi-Pyrénées. Size 31 x 16 x15 cm. Photo by Didier Descouens. Licensed under CC By-SA 3.0.
While marble will effervesce when exposed to hydrochloric acid, anhydrite will not. An acid test may help distinguish carved or crystal anhydrites from marble items that may appear similar. However, keep in mind that acid testing is a destructive technique. Conduct this examination only as a last resort on an inconspicuous part of the object.
Anhydrite has many practical applications. Like its more abundant “alter ego,” gypsum, it’s used in a variety of construction materials as well as fertilizers. However, it exceeds gypsum in both calcium content and solubility, so it makes a better soil treatment. Thus, there is an industrial demand to synthesize this material. However, there is no known jewelry use for it.
Once considered a “nuisance product” from the manufacture of hydrochloric acid, synthetic anhydrite created from this process is now dried in kilns and used for many applications. The English sculptor Ophelia Gordon Bell carved this plaque depicting an anhydrite kiln from a piece of anhydrite. The carving now resides at the Catalyst Science Discovery Centre in Widnes, UK. Picture by and © Andy Mabbett. Licensed under CC By-SA 4.0.
Blue and violet colors in anhydrites disappear when heat treated. However, gamma ray bombardment will restore them. Therefore, these colors possibly occur naturally due to natural radiation in the earth. Please note, natural specimens aren’t radioactive or harmful.
Notable sources of gem-quality material include the following:
A large, pastel blue anhydrite specimen. 11.8 x 9.0 x 5.8 cm. Naica, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
Unusual faceted anhydrites usually range on the small size (1-5 carats). However, faceters have cut gems up to 9 carats, so the potential exists for larger sizes. Cleavage masses could provide larger rough.
Swiss and Canadian localities produce most of the faceted material, usually in purplish or pale pink colors.
Due to their cleavage and relatively low hardness, anhydrites must be cut and handled with great care. For jewelry, avoid ring use and use protective settings if possible. Consider creating earrings, pendants, and bracelets, instead. Of course, carvings and decorative objects will hopefully face fewer risks.
Keep any anhydrites dry, especially if placed in storage. They will readily absorb moisture and, over time, turn wholly or partly into gypsum.
Don’t wipe dust off anhydrites. Since household dust consists mostly of silicon quartz, which is far harder (7) than anhydrites, you’ll scratch them. Pat them with a lint-free cloth, instead.
For more recommendations, consult our gemstone jewelry care guide.
Anhydrite: Germany (6.1). © Joel E. Arem, PhD, FGA. Used with permission.
Gemstone cleavage is a break in a crystal along internal planes. Learn the science behind this and the difference between cleavage, fracture,…
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