| Khomyakovite | |
| Category: | Silicate mineral, cyclosilicate |
| Formula: | (original form) |
| Imasymbol: | Kmy[1] |
| Strunz: | 9.CO.10 (10 ed) 8/E.23-30 (8 ed) |
| Dana: | 64.1.2.5 |
| System: | Trigonal |
| Class: | Ditrigonal pyramidal (3m) H-M symbol: (3m) |
| Symmetry: | R3m |
| Unit Cell: | a = 14.30, c = 30.08 [Å] (approximated); Z = 3 |
| Color: | Orange to orange-red |
| Habit: | Aggregates (anhedral to subhedral) |
| Cleavage: | None |
| Fracture: | Uneven |
| Tenacity: | Brittle |
| Mohs: | 5–6 |
| Luster: | Vitreous |
| Streak: | White |
| Diaphaneity: | Transparent to translucent |
| Density: | 3.14 (calculated) |
| Opticalprop: | Uniaxial (−) |
| Refractive: | nω = 1.63, nε = 1.63 (approximated) |
| Pleochroism: | None |
Khomyakovite is an exceedingly rare mineral of the eudialyte group, with formula .[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. 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).
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.
Impurities in khomyakovite include niobium, potassium and manganese, with minor rare earth elements, magnesium, titanium, hafnium and aluminium.