Almandine

Almandine
Almandine
General
Category	Nesosilicate
Formula; (repeating unit)	Fe2+; 3Al; 2Si; 3O; 12
IMA symbol	Alm
Strunz classification	9.AD.25
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) ; H–M symbol: (4/m 3 2/m)
Space group	Ia3d
Identification
Color	reddish orange to red, slightly purplish red to reddish purple and usually dark in tone
Cleavage	none
Fracture	conchoidal
Mohs scale hardness	7.0–7.5
Luster	greasy to vitreous
Streak	white
Specific gravity	4.05+0.25; −0.12
Polish luster	vitreous to subadamantine
Optical properties	Single refractive, and often anomalous double refractive
Refractive index	1.790±0.030
Birefringence	none
Pleochroism	none
Dispersion	0.024
Ultraviolet fluorescence	inert
Absorption spectra	usually at 504, 520, and 573 nm, may also have faint lines at 423, 460, 610 and 680–690 nm
References

Almandine (/ˈælməndɪn/), also known as almandite, is a species of mineral belonging to the garnet group. The name is a corruption of alabandicus, which is the name applied by Pliny the Elder to a stone found or worked at Alabanda, a town in Caria in Asia Minor. Almandine is an iron alumina garnet, of deep red color, inclining to purple. It is frequently cut with a convex face, or en cabochon, and is then known as carbuncle. Viewed through the spectroscope in a strong light, it generally shows three characteristic absorption bands.^[6]

Almandine is one end-member of a mineral solid solution series, with the other end member being the garnet pyrope. The almandine crystal formula is: Fe₃Al₂(SiO₄)₃. Magnesium substitutes for the iron with increasingly pyrope-rich composition.

Almandine, Fe²⁺
₃Al
₂Si
₃O
₁₂, is the ferrous iron end member of the class of garnet minerals representing an important group of rock-forming silicates, which are the main constituents of the Earth's crust, upper mantle and transition zone. Almandine crystallizes in the cubic space group Ia3d, with unit-cell parameter a ≈ 11.512 Å at 100 K.^[7]

Almandine is antiferromagnetic with the Néel temperature of 7.5 K. It contains two equivalent magnetic sublattices.^[8]

^ 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 ^c ^d ^e ^f ^g Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6
^ Mindat.org - Almandine
^ Webmineral.com - Almandine
^ "Handbook of Mineralogy - Almandine" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2013-03-01.
^ One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Almandine". Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 712.
^ Geiger, C.; Armbruster, Th.; Lager, G.; Jiang, K.; Lottermoser, W.; Amthauer, G. (1992). "A combined temperature dependent ⁵⁷Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii–Karyagin effect". Physics and Chemistry of Minerals. 19 (2): 121–126. doi:10.1007/BF00198609. S2CID 98610041.
^ Zherebetskyy, Danylo (2010). Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates (PhD). Dissertation.com, Boca Raton, Florida. ISBN 978-1-59942-316-6.

[1] 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.

[GRG-2] ^ ^a ^b ^c ^d ^e ^f ^g Gemological Institute of America, GIA Gem Reference Guide 1995, ISBN 0-87311-019-6

[3] Mindat.org - Almandine

[4] Webmineral.com - Almandine

[5] "Handbook of Mineralogy - Almandine" (PDF). Archived from the original (PDF) on 2016-03-03. Retrieved 2013-03-01.

[EB1911-6] One or more of the preceding sentences incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Almandine". Encyclopædia Britannica. Vol. 1 (11th ed.). Cambridge University Press. p. 712.

[Paper_1-7] Geiger, C.; Armbruster, Th.; Lager, G.; Jiang, K.; Lottermoser, W.; Amthauer, G. (1992). "A combined temperature dependent ⁵⁷Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii–Karyagin effect". Physics and Chemistry of Minerals. 19 (2): 121–126. doi:10.1007/BF00198609. S2CID 98610041.

[Thesis-8] Zherebetskyy, Danylo (2010). Quantum mechanical first principles calculations of the electronic and magnetic structure of Fe-bearing rock-forming silicates (PhD). Dissertation.com, Boca Raton, Florida. ISBN 978-1-59942-316-6.

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