single crystal (4.2cm) - Diakon, Nioro du Sahel Circle, Kayes Region, Mali
Category Garnet group
Chemical formula Ca3Fe2(SiO4)3
Crystal symmetry Isometric 4/m 3 2/m
Unit 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
Crystal system Cubic - Hexoctahedral
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 - 440nm band or complete absorption at 440nm and below, may also have lines at 618, 634, 685, 690nm [1]
References [1][2][3][4]
Major varieties
Demantoid transparent light to dark green to yellow-green
Melanite opaque black
Topazolite transparent to translucent yellow, may show chatoyancy

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

Andradite includes three varieties:

  • Melanite: Black in color, referred to as "titanian andradite".[5]
  • Demantoid: Vivid green in color, one of the most valuable and rare stones in the gemological world.
  • Topazolite: Yellow-green in color and sometimes of high enough quality to be cut into a faceted gemstone.

It was first described in 1868 for an occurrence in Drammen, Buskerud, Norway.[3] Andradite was named after the Brazilian mineralogist José Bonifácio de Andrade e Silva (1763–1838).[2]


Black crystals of andradite : melanite

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.[2] It is found in Italy, the Ural Mountains of Russia, Arizona and California and in Dnipropetrovsk Oblast in Ukraine.

As the other garnets andradite crystallizes in the cubic space group [[Ia3d]], with unit-cell parameter of 12.051 Å at 100 K.[6]

The spin structure of andradite contains two mutually canted equivalent antiferromagnetic sublattices [7] below the Néel temperature (TN=11 K [8]).


  1. ^ a b Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
  2. ^ a b c Handbook of Mineralogy
  3. ^ a b
  4. ^ Webmineral data
  5. ^ Mindat
  6. ^ 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.
  7. ^ Danylo Zherebetskyy (2010). Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates, PhD Thesis, Universal Publishers/, Boca Raton, Florida, USA, p. 136. ISBN 1599423162.
  8. ^ Enver Murad (1984): Magnetic ordering in andradite. American Mineralogist 69, no. 7-8; p. 722-724.

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Look at other dictionaries:

  • Andradite — Andradite[1] Catégorie IX : silicates[2] …   Wikipédia en Français

  • andradite — ● andradite nom féminin (de Andrada e Silva, nom propre) Grenat calcique. ⇒ANDRADITE, subst. fém. MINÉR. Variété de grenat noir composée de fer et de calcium : • ... enfin la mélanite, noire comme son nom l indique, fut le membre le plus méprisé… …   Encyclopédie Universelle

  • andradite — [an′drə dīt΄] n. [after J. B. de Andrada ( c. 1763 1838), Brazilian geologist] a variety of garnet, Ca3Fe2 (SiO4) 3, sometimes used as a gem …   English World dictionary

  • andradite — /an dreuh duyt /, n. a mineral, calcium iron garnet, Ca3Fe2Si3O2, occurring in brown, green, or black crystals. [1830 40; named after J. B. de ANDRADA E SILVA; see ITE1] * * * ▪ gemstone  calcium iron garnet, perhaps the most spectacular garnet… …   Universalium

  • andradite — andraditas statusas T sritis chemija apibrėžtis Granatų grupės mineralas. formulė Ca₃Fe₂[SiO₄]₃ atitikmenys: angl. andradite rus. андрадит …   Chemijos terminų aiškinamasis žodynas

  • andradite — noun Etymology: José B. de Andrada e Silva died 1838 Brazilian geologist Date: 1868 a calcium iron garnet occurring in various colors ranging from yellow and green to brown and black …   New Collegiate Dictionary

  • andradite — noun A nesosilicate mineral of the garnet group with chemical formula CaFeSiO …   Wiktionary

  • andradite — an·dra·dite …   English syllables

  • andradite — an•dra•dite [[t]ˈæn drəˌdaɪt[/t]] n. mir a garnet occurring in brown, green, or black crystals • Etymology: 1830–40; after J. B. de Andrada e Silva; see ite I …   From formal English to slang

  • andradite — /ˈændrədaɪt/ (say andruhduyt) noun a mineral, calcium iron garnet, Ca3Fe2Si3O12, occurring in brown, green, or black crystals. {named after José Bonifacio d Andrada e Silva, 1763–1838, Brazilian mineralogist. See ite1} …  

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