Nesosilicate mineral species of garnet
Andradite [Adr] Single crystal (4.2 cm) – Diakon, Nioro du Sahel Circle, Kayes Region, Mali
Category Garnet groupFormula (repeating unit) Ca3 Fe2 (SiO4 )3 IMA symbol Adr[ 1] Strunz classification 9.AD.25 Crystal system Cubic Crystal class Hexoctahedral (m3 m) H-M symbol : (4/m 3 2/m) Space group I a3 dUnit cell a = 12.056 Å; Z = 8 Color Yellow, greenish yellow to emerald-green, dark green; brown, brownish red, brownish yellow; grayish black, black; may be sectored Crystal habit Commonly well-crystallized dodecahedra, trapezohedra, or combinations, also granular to massive Cleavage none Fracture conchoidal to uneven Tenacity Brittle Mohs scale hardness 6.5 to 7 Luster Adamantine to resinous, dull Streak White Diaphaneity Transparent to translucent Specific gravity 3.859 calculated; 3.8–3.9 measured Optical properties Isotropic, typically weakly anisotropic Refractive index n = 1.887 Absorption spectra demantoid – 440 nm band or complete absorption at 440 nm and below, may also have lines at 618, 634, 685, 690 nm[ 2] References [ 2] [ 3] [ 4] [ 5] Demantoid transparent light to dark green to yellow-green Melanite opaque black Topazolite transparent to translucent yellow, may show chatoyancy
Andradite is a mineral species of the garnet group . It is a nesosilicate , with formula Ca3 Fe2 Si3 O12 .
Andradite includes three varieties:
Colophonite [ 6] : 61 Demantoid gemological world.[ 7] 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.[ 8] Topazolite : Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone , it is rarer than demantoid.[ 7] It was first described in 1868 for an occurrence in Drammen , Buskerud , Norway .[ 3] [ 4] [ 7] Brazilian statesman, naturalist, professor and poet José Bonifácio de Andrada e Silva (1763–1838).[ 3] [ 7]
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] 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 [[Ia3 d]], with unit-cell parameter of 12.051 Å at 100 K.[ 9]
The spin structure of andradite contains two mutually canted equivalent antiferromagnetic sublattices[ 10] Néel temperature (TN =11 K[ 11]
See also
References
^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols" . Mineralogical Magazine . 85 (3): 291– 320. Bibcode :2021MinM...85..291W . doi :10.1180/mgm.2021.43 S2CID 235729616 . ^ a b Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
^ a b c d Handbook of Mineralogy ^ a b Andradite , Mindat.org^ Webmineral data ^ Olga Bortnik . All about precious stones. ― Moscow: Harvest, 2011.^ a b c d Grande, Lance; Augustyn, Allison (2009). Gems and Gemstones: Timeless Natural Beauty of the Mineral World 188– 91. ISBN 978-0-226-30511-0 ^ Melanite , Mindat.org^ 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.
^ Danylo Zherebetskyy (2010). Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates Universal Publishers /Dissertation.com, Boca Raton, Florida, USA, p. 136. ISBN 1-59942-316-2 .
^ Enver Murad (1984): "Magnetic ordering in andradite ." American Mineralogist 69, no. 7-8; pp. 722–24.
External links
Andradite at Wikimedia Commons
Forms Making
Materials
Terms
