Andradite

 ( Calcium Minerals ) 

Andradite is a Mineralogy species of the Garnet. It is a nesosilicate, with formula Ca₃Fe₂Si₃O₁₂.

Andradite includes three varieties:

• Colophonite: a historical variety found in the Scandinavian islands, brownish or reddish in color, often opaque or translucent. Olga Bortnik. All about precious stones. ― Moscow: Harvest, 2011.
• Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemology world.
  (2025). 9780226305110, University of Chicago Press. . ISBN 9780226305110
• Melanite: Black in color due to limited substitution of titanium for iron. Also known as "titanian andradite". Forms a solid solution with morimotoite and schorlomite depending on titanium and iron content. Melanite, Mindat.org
• Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone, it is rarer than demantoid.

It was first described in 1868 for an occurrence in Drammen, Buskerud, Norway. Andradite was named after the statesman, naturalist, professor and poet José Bonifácio de Andrada e Silva (1763–1838).

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Occurrence It occurs in developed in contact metamorphosed impure or calcic ; in chlorite and and in alkalic (typically Titanium). Associated minerals include vesuvianite, Chlorite group, epidote, spinel, calcite, dolomite and magnetite. It is found in Iran, Italy, the Ural Mountains of Russia, Arizona and California and in Dnipropetrovsk Oblast in Ukraine.

Like the other garnets, andradite crystallizes in the cubic space group 3}}d, with unit-cell parameter of 12.051 Å at 100 K.Thomas Armbruster and Charles A. Geiger (1993): " Andradite crystal chemistry, dynamic X-site disorder and structural strain in silicate garnets." European Journal of Mineralogy v. 5, no. 1, p. 59-71.

The spin structure of andradite contains two mutually canted equivalent antiferromagnetic sublatticesDanylo Zherebetskyy (2010). Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates, PhD Thesis, Universal Publishers/Dissertation.com, Boca Raton, Florida, USA, p. 136. . below the Néel temperature (T_N=11 KEnver Murad (1984): " Magnetic ordering in andradite." American Mineralogist 69, no. 7-8; pp. 722–24.).

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See also

• Almandine
• Geology
• Grossular
• Mineral
• Mineral collecting
• Pyrope
• Spessartine
• Tsavorite
• Uvarovite

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External links

Categories: Calcium Minerals, Iron Minerals, Garnet Gemstones, Minerals In Space Group 230, Titanium Minerals, Minerals Described In 1868

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