Английская Википедия:Andradite

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Шаблон:Short description Шаблон:Infobox mineral

Andradite is a mineral species of the garnet group. It is a nesosilicate, with formula Ca3Fe2Si3O12.

Andradite includes three varieties:

  • 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.[1]
  • Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world.[2]
  • Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone, it is rarer than demantoid.[2]

It was first described in 1868 for an occurrence in Drammen, Buskerud, Norway.[3][4][2] Andradite was named after the Brazilian statesman, naturalist, professor and poet José Bonifácio de Andrada e Silva (1763–1838).[3][2]

Occurrence

It occurs in skarns developed in contact metamorphosed impure limestones or calcic igneous rocks; in chlorite schists and serpentinites and in alkalic igneous rocks (typically titaniferous). Associated minerals include vesuvianite, chlorite, epidote, spinel, calcite, dolomite and magnetite.[3] 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 [[IaШаблон:Overlined]], with unit-cell parameter of 12.051 Å at 100 K.[5]

The spin structure of andradite contains two mutually canted equivalent antiferromagnetic sublattices[6] below the Néel temperature (TN=11 K[7]).

See also

Шаблон:Col div

Шаблон:Col div end

References

Шаблон:Reflist

External links

Шаблон:Commonscatinline Шаблон:Titanium minerals Шаблон:Jewellery

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  1. ↑ Melanite, Mindat.org
  2. ↑ 2,0 2,1 2,2 2,3 Шаблон:Cite book
  3. ↑ 3,0 3,1 3,2 Ошибка цитирования Неверный тег <ref>; для сносок Handbook не указан текст
  4. ↑ Ошибка цитирования Неверный тег <ref>; для сносок Mindat не указан текст
  5. ↑ 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.
  6. ↑ Danylo 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. Шаблон:ISBN.
  7. ↑ Enver Murad (1984): "Magnetic ordering in andradite." American Mineralogist 69, no. 7-8; pp. 722–24.
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