Ettringite
Image: <a href="//commons.wikimedia.org/wiki/User:Archaeodontosaurus" title="User:Archaeodontosaurus">Didier Descouens</a> (CC BY-SA 3.0)
Mineral NameEttringite
Chemical FormulaCa₆Al₂(SO₄)₃(OH)₁₂·26H₂O
Mohs Hardness2.5
Crystal Systemhexagonal
Lustervitreous
Streak Colorwhite
Cleavageperfect on {1010}
Fractureuneven
Specific Gravity1.78
Colorsyellow, white
Transparencytranslucent
Type LocalityN'Chwaning Mines, Kalahari manganese fields, Northern Cape Province, South Africa
Mineral Groupsulfates
Usescollector
Associated Mineralsrhodochrosite, hausmannite, braunite
Rarityuncommon
Description
This specimen features vibrant yellow, prismatic to acicular ettringite crystals, some appearing blocky, growing on a reddish-brown matrix with some white associated minerals.
Geological Context
Ettringite typically forms in low-temperature hydrothermal veins, often found in oxidized zones of manganese ore deposits or metamorphosed limestones, as is the case in the Kalahari manganese fields.
