Mineralpedia Details for Amesite

Amesite

Named to honor mine owner James Ames. Amesite is a rare mineral that is the result of the low-grade metamorphism of aluminum and magnesium rich rocks. It can be found in localities in the United States, Canada, Antarctica, South Africa, Russia, Sweden, and Poland, among several others. Assocaited minerals include vesuvianite, chlorite, magnetite, rutile, diaspore, grossular, calcite, diopside, and clinozoisite.

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

Formula: Mg₂Al(SiAl)O₅(OH)₄
Crystal System: Triclinic
Crystal Habit: Micaceous, Foliated, Pseudo Hexagonal
Cleavage: Perfect, None, None
Luster: Pearly
Color: white, light green
Streak: pale green
Class: Triclinic - Pedial
Hardness: 2.5-3
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Amesite (chromian) from Saranovskii mine, Urals Region, Russia

It is a phyllosilicate and a member of the serpentine group. In this case it is colored purple by chromium, which is non-essential to the chemical composition. The crystals are pseudo-hexagonal and somewhat tapering like a tornado. The fun thing about this occurence is that the Amesite is color-changing. In sun-light it is a dull grey, but in incandescent lighting it is a beautiful purple.