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Mineral of the eudialyte group From Wikipedia, the free encyclopedia
Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2.[2][3] The original formula was extended to show the presence of both the cyclic silicate groups and M4-site silicon, according to the nomenclature of the eudialyte group.[4] Some niobium substitutes for tungsten in khomyakovite. Khomyakovite is an iron-analogue of manganokhomyakovite, the second mineral being a bit more common.[3] The two minerals are the only group representatives, beside taseqite, with species-defining strontium, although many other members display strontium diadochy. Khomyakovite is the third eudialyte-group mineral with essential tungsten (after johnsenite-(Ce) and manganokhomyakovite).[2]
Khomyakovite | |
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General | |
Category | Silicate mineral, cyclosilicate |
Formula (repeating unit) | Na12Sr3Ca6Fe3Zr3W(Si25O73)(O,OH,H2O)3(OH,Cl)2 (original form) |
IMA symbol | Kmy[1] |
Strunz classification | 9.CO.10 (10 ed) 8/E.23-30 (8 ed) |
Dana classification | 64.1.2.5 |
Crystal system | Trigonal |
Crystal class | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
Space group | R3m |
Unit cell | a = 14.30, c = 30.08 [Å] (approximated); Z = 3 |
Identification | |
Color | Orange to orange-red |
Crystal habit | Aggregates (anhedral to subhedral) |
Cleavage | None |
Fracture | Uneven |
Tenacity | Brittle |
Mohs scale hardness | 5–6 |
Luster | Vitreous |
Streak | White |
Diaphaneity | Transparent to translucent |
Density | 3.14 (calculated) |
Optical properties | Uniaxial (−) |
Refractive index | nω = 1.63, nε = 1.63 (approximated) |
Pleochroism | None |
References | [2][3] |
Khomyakovite, manganokhomyakovite, johnsenite-(Ce) and oneillite are four eudialyte-group minerals with type locality in Mont Saint-Hilaire, Quebec, Canada.[5] Khomyakovite itself is associated with analcime, annite, natrolite, titanite, calcite, and pyrite.[3]
Impurities in khomyakovite include niobium, potassium and manganese, with minor rare earth elements, magnesium, titanium, hafnium and aluminium.[3]
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