Ettringite
Ettringite is not generally facetable; any cut stone would be considered an extreme rarity. South African material has yielded minute stones, some of which may have been labeled sturmanite.
Series to Sturmanite.
Optics: o = 1.491; e = 1.470.
Uniaxial (-).
Occurrence: At type locality (Ettringen, Rhine Province, Germany) in cavities of metamorphosed limestone inclusions in alkaline igneous rocks. Also in metamorphosed limestones.
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.
Comments: Ettringite is not generally facetable; any cut stone would be considered an extreme rarity. South African material has yielded minute stones, some of which may have been labeled sturmanite.
Name: After the locality in Germany.