Khomyakovite
Mineral of the eudialyte group
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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]
8/E.23-30 (8 ed)
| Khomyakovite | |
|---|---|
| |
| General | |
| Category | Silicate mineral, cyclosilicate |
| Formula | 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] |
Occurrence and association
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]
