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Mineralpedia Details for Ettringite

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Ettringite

Ettringite

Named for the type localities in Mayner Feld and Ettringer Feld in the Northern and Southern lava flows of the Bellerberg volcano in Ettringen in Rhineland-Pfalz, Germany. Additional localities for Ettringite include in France, Ireland, Israel, South Africa, the United States, and a few others. In its Israeli locality in the Hatrurim Formation, it occurs in metamorphosed limestone near contacts with igneous rocks and in xenoliths and as a crust on weathered larnites. Associated minerals include portlandite, afwillite, hydrocalumite, mayenite, and gypsum.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/ettringite.pdf

Formula
Ca6Al2(SO4)3(OH)12ยท26H2
Crystal System
Hexagonal 
Crystal Habit
Acicular 
Cleavage
Perfect, None, None 
Luster
Vitreous (Glassy) 
Color
colorless, white 
Streak
white 
Class
Hexagonal - Dihexagonal Dipyramidal 
Hardness
2-2.5 
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Ettringite from Commercial quarry, Crestmore, Riverside Co., California, United States

Ettringite
            from Commercial quarry, Crestmore, Riverside Co., California, United States

Light yellow crusts and micro crystals. The micro crystals measure about 0.75mm.

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Ettringite from N'Chwaning II mine, Kalahari Mn fields, Northern Cape Province, South Africa

Ettringite
            from N'Chwaning II mine, Kalahari Mn fields, Northern Cape Province, South Africa

Yellow, translucent prismatic crytals to 9mm. Information on Mindat indicates that this mineral has been found as a synthetic phase in concrete and a potential product for the immobilisation of toxic metals. Mostly is found as white to clear micro crystals naturally and in slag dumps worldwide. Yellow crystals like these from this mine are probably the largest and and best color in the world.

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