Ettringite Value, Price, and Jewelry Information

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Ettringite crystal, 5.0 x 3.5 x 2.0 cm, N'Chwaning Mines, Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa. © Rob Lavinsky, www.iRocks.com. Used with permission.

Ettringite is not generally facetable. Any cut stone would be considered an extreme rarity.

Ettringite Information

Data Value
Name Ettringite
Colors Colorless to light yellow, milky.
Hardness 2-2.5
Cleavage Perfect, rhombohedral
Formula Ca6AI2(SO4)3(OH)1224H2O
Crystallography Hexagonal; usually flattened hexagonal dipyramids; sometimes prismatic, fibrous.
Refractive Index 1.470-1.491
Birefringence 0.021
Luminescence None
Luminescence Present No
Absorption Spectrum Not diagnostic
Pleochroism None; colorless in transmitted light; dehydrates and turns white.
Optics = 1.491; = 1.470. Uniaxial (-).
Optic Sign Uniaxial -
Luster Vitreous
Specific Gravity 1.77
Transparency Transparent to translucent
Etymology After the locality in Germany.
Occurrence At type locality (Ettringen, Rhine Province, Germany) in cavities of metamorphosed limestone inclusions in alkaline igneous rocks. Also in metamorphosed limestones.

Comments

South African material has yielded minute stones, some of which may have been labeled sturmanite.

Series to Sturmanite.

Sources

Ettringen, Germany: In tiny crystals.

Franklin, New Jersey: Minute crystals.

South Africa: Associated with sturmanite at the Jwaneng mine, near Hotazel. The sturmanite forms yellowish coatings, with ettringite cores.

Stone Sizes

Material from Ettringen and Franklin is microscopic. A 2.5 carat pale yellow ettringite was faceted from material found in the center of a mass of sturmanite from South Africa. This may be the largest known for the species.

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