Custom cushion-cut celestite, 5.12 cts, 10.6 x 8.9 mm, Madagascar. © The Gem Trader. Used with permission.
Soft, fragile, and hard to cut, celestite or celestine is seldom seen in gem collections. Large, clean faceted celestites are very rare. These gems are usually colorless or pale blue, but rare orange, green, yellow, and red shades have also been found.
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| Data | Value |
|---|---|
| Name | Celestite |
| Crystallography | Orthorhombic, Crystals common, usually tabular; also nodules, earthy, massive. |
| Refractive Index | 1.622-1.635 |
| Colors | Colorless, white, gray, blue, green, yellow, orange, and red shades. |
| Luster | Vitreous; pearly on cleavage. |
| Hardness | 3-3.5 |
| Fracture | Uneven |
| Specific Gravity | 3.97-4.00 |
| Birefringence | 0.009-0.012 |
| Cleavage | Perfect 1 direction, good 1 direction |
| Dispersion | 0.014 |
| Heat Sensitivity | Yes |
| Luminescence | Blue in SW. Blue or dull yellow in LW. May phosphoresce blue-white. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, Phosphorescent, UV-Long, UV-Short |
| Transparency | Transparent |
| Absorption Spectrum | Not diagnostic |
| Formula | SrSO4 |
| Pleochroism | Weak, in shades of indigo blue, bluish green, and violet. |
| Optics | a = 1.622 – 1.625; β = 1.624; γ = 1.631 -1.635. Biaxial (+), 2V = 50° |
| Optic Sign | Biaxial + |
| Etymology | From the Latin coelestis for “celestial,” in allusion to the delicate and lovely pale blue color often displayed by this mineral. |
| Occurrence | Celestite occurs in sedimentary rocks, especially limestones; it is also found in hydrothermal vein deposits, sometimes in igneous rocks. |
| Inclusions | Single phase, liquid inclusions; partially healed fractures. |
Celestites in a geode, Sakoany deposit, Katsepy Commune, Mitsinjo District, Boeny Region, Mahajanga Province, Madagascar. © Rob Lavinsky, www.iRocks.com. Used with permission.
The minerals barite and celestite form a series. Baryte lies at the barium (Ba) end; celestite at the strontium (Sr) end. This mineral is a major source of strontium.
While transparent crystals aren’t rare per se, facetable gem-quality material is quite rare. Faceted gems show little dispersion.
Celestine crystal (celestite), Bull Creek, near Austin, Travis County, Texas, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
Gems from Madagascar have refractive indices as follows: a = 1.619; γ = 1.631.
None known.
Blue gems may fade because of heat or light, but irradiation may restore the color.
Canada produces rare orange crystals. Tsumeb, Namibia also yields gem-quality material.
Celestite: Canada (1.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Celestite gems, usually colorless or pale blue, typically weigh under three carats and often receive step cuts. However, some gems are known in the 30-carat range. Large, transparent crystals may be found and cut.
Put-in-Bay, Ohio boasts the Crystal Cave, “the world’s largest geode.” Converted into a cave, the 35′ wide geode contains celestite crystals up to 18” across.
Celestite crystals, Crystal Cave, Put-in-Bay, Ohio. Photo by James St. John. Licensed under CC By 2.0.
Due to its softness, perfect cleavage, and light sensitivity, this gem makes a better collector’s item than a jewelry piece. Celestites also have great heat sensitivity. Since jeweler’s torches can easily exceed 200° C (392° F) and cause the stone’s colors to fade, be wary if you take a jewelry piece to be repaired. Consult our gemstone jewelry cleaning guide for more recommendations.
Celestite: Madagascar (16.3). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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