Eudialyte
Eudialyte | |
---|---|
General | |
Category | Cyclosilicate |
Formula (repeating unit) |
Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3 (Si3O9)2(Si9O27)2(OH,Cl)2 |
Strunz classification | 09.CO.10 |
Crystal symmetry |
Trigonal - hexagonal scalenohedral H-M symbol: (32/m) Space group: R3m |
Identification | |
Color | Red, magenta, brown; also blue and yellow |
Crystal habit | Crystals short rhombohedral to long prismatic, granular, irregular masses |
Crystal system | Trigonal |
Cleavage | Distinct on {0001} imperfect on {1120} |
Fracture | Uneven |
Tenacity | Brittle |
Mohs scale hardness | 5 - 6 |
Luster | Vitreous |
Streak | White |
Diaphaneity | Transparent to translucent |
Specific gravity | 2.74–3.10 |
Optical properties | Uniaxial (+/-) |
Refractive index | nω = 1.606–1.610 nε = 1.610–1.613 |
Birefringence | δ = 0.004 |
Pleochroism | Weak: O= colorless, pale yellow, pink; E= pink to colorless |
Solubility | H2SO4 |
Other characteristics | Mildly Radioactive |
References | [1][2][3] |
Eudialyte, whose name derives from the Greek phrase Εὖ διάλυτος eu dialytos, meaning "well decomposable", is a somewhat rare, red silicate mineral, which forms in alkaline igneous rocks, such as nepheline syenites. Its name alludes to its ready solubility in acid.[1][3]
Eudialyte was first described in 1819 for an occurrence in nepheline syenite of the Ilimaussaq intrusive complex of southwest Greenland.[1]
Uses of eudialyte
Eudialyte is used as a minor ore of zirconium. Another use of eudialyte is as a minor gemstone, but this use is limited by its rarity, which is compounded by its poor crystal habit. These factors make eudialyte of primary interest as a collector's mineral.
Associated minerals
Eudialyte is found associated with other alkalic igneous minerals, in addition to the some minerals common to most igneous material in general.
Associate minerals include: microcline, nepheline, aegirine, lamprophyllite, lorenzenite, murmanite, arfvedsonite, sodalite, aenigmatite, rinkite, låvenite, titanite and titanian magnetite.[2]
Alternative names
Alternative names of eudialyte include: almandine spar and eudalite. Eucolite is the name of an altered form.
Notes for identification
Eudialyte's rarity makes locality useful in its identification. Prominent localities of eudialyte include Mont Saint-Hilaire in Canada and the Kola Peninsula in Russia, but it is also found in Greenland, Norway, and Arkansas. The lack of crystal habit, associated with color, is also useful for identification, as are associated minerals. A pink-red mineral with no good crystals associated with other alkaline igneous material, especially nepheline and aegirine, is a good indication a specimen is eudialyte.
Eudialyte group
Microchemical (by electron microprobe) and structural analyzes of different eudialyte (and related) samples revealed presence of many new eudialyte-like minerals. These minerals are structurally and chemically related and joined into eudialyte group. The group includes Zr-, OH-, Cl-, F-, CO3- and possibly also SO4-bearing silicates of Na, K, H3O, Ca, Sr, REEs, Mn, Fe, Nb and W. Electron vacancies can be present in their structure, too.
References
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