Eudialyte

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Eudialyte
Eudialyte.jpg
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 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, nine member ring cyclosilicate 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[edit]

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. Eudialyte typically has a significant content of U, Pb, Nb, Ta, Zr, Hf, and rare earth elements (REE). Because of this, it is very common geoscientists use eudialyte as a geochronometer to date and investigate the genesis of the host rocks.[4]

Associated minerals[edit]

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, catapleiite, murmanite, arfvedsonite, sodalite, aenigmatite, rinkite, låvenite, titanite and titanian magnetite.[2]

Alternative names[edit]

Alternative names of eudialyte include: almandine spar, eudalite, Saami blood.[1] Eucolite is the name of an optically negative variety, more accurately the group member: ferrokentbrooksite.[5]

Notes for identification[edit]

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[edit]

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[edit]

  1. ^ a b c d Eudialyte on Mindat.org
  2. ^ a b Handbook of Mineralogy
  3. ^ a b Eudialyte on Webmineral
  4. ^ Wu, F.-Y., Yang, Y.-H., Marks, M.A.W., Liu, Z.-C., Zhou, Q., Ge, W.-C., Yang, J.-S., Zhao, Z.-F., Mitchell, R.H., Markl, G., 2010. In situ U-Pb, Sr, Nd and Hf isotopic analysis of eudialyte by LA-(MC)-ICP-MS. Chemical Geology 273, 8–34. [1]
  5. ^ Eucolite on Mindat