Eudialyte

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Eudialyte
General
CategoryCyclosilicate
Formula
(repeating unit)
Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3
(Si3O9)2(Si9O27)2(OH,Cl)2
Strunz classification09.CO.10
Crystal symmetryTrigonal - hexagonal scalenohedral
H-M symbol: (32/m)
Space group: R3m
Identification
ColorRed, magenta, brown; also blue and yellow
Crystal habitCrystals short rhombohedral to long prismatic, granular, irregular masses
Crystal systemTrigonal
CleavageDistinct on {0001} imperfect on {1120}
FractureUneven
TenacityBrittle
Mohs scale hardness5 - 6
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.74 - 3.10
Optical propertiesUniaxial (+/-)
Refractive indexnω = 1.606 - 1.610 nε = 1.610 - 1.613
Birefringenceδ = 0.004
PleochroismWeak: O= colorless, pale yellow, pink; E= pink to colorless
SolubilityH2SO4
Other characteristicsMildly Radioactive
References[1][2][3]
 
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Eudialyte
General
CategoryCyclosilicate
Formula
(repeating unit)
Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3
(Si3O9)2(Si9O27)2(OH,Cl)2
Strunz classification09.CO.10
Crystal symmetryTrigonal - hexagonal scalenohedral
H-M symbol: (32/m)
Space group: R3m
Identification
ColorRed, magenta, brown; also blue and yellow
Crystal habitCrystals short rhombohedral to long prismatic, granular, irregular masses
Crystal systemTrigonal
CleavageDistinct on {0001} imperfect on {1120}
FractureUneven
TenacityBrittle
Mohs scale hardness5 - 6
LusterVitreous
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.74 - 3.10
Optical propertiesUniaxial (+/-)
Refractive indexnω = 1.606 - 1.610 nε = 1.610 - 1.613
Birefringenceδ = 0.004
PleochroismWeak: O= colorless, pale yellow, pink; E= pink to colorless
SolubilityH2SO4
Other characteristicsMildly Radioactive
References[1][2][3]
Eudialyte in syenite, Brazil. The white mineral is alkali feldspar, the black is aegirine, and the little brown bits are biotite.

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]

Contents

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