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Ettringite

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MGR926415

Ettringite

Classic Locality

Description Tabs

Description
Locality: 
NChwaning II Mine, Kuruman, Kalahari, Northern Cape Province, South Africa
Class: 
Crystals on Matrix
Size Range: 
Miniature (4.5-7 cm)
Size: 
4.8 × 2.7 × 1.8 cm
Description

You all know this bright yellow crystals - now looks at this piece - it seems to consist of sharp discs. It is not pure Ettringite - this is a mineralogical oddity. The is only a minor chemical difference between Ettringite and Sturmanite. While ago - before science recognize the difference - Ettringite was labeled as Sturmanite and even today you will find photos from earlier years or descriptions or pieces in old collections labeled as Sturmanite, which are in fact Ettringite. And this crystal unify both compounds - the darker discs are Sturmanite, the the lighter discs are Ettringite. This is really an amazing sample - I know only a fist full of pieces from only one small discovery!

The crystal is set on the typical almost black matrix, it is complete all around with some minor inter-grown matrix. The end-points are mostly sharp, only one side seems to have no more room (but that´s really small).

Mineral Data
What's on the rock

Ettringite

Formula: 
Ca6Al2(SO4)3(OH)12·26H2O
Strunz: 
7.DG.15
Hardness: 
2.0 - 2.5
Type Locality: 
Ettringer Feld, Western lava flow, Bellerberg volcano, Ettringen, Mayen, Eifel, Rhineland-Palatinate, Germany