Eudialyte

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
Eudialyte-163974.jpg
General
CategoryCyclosilicate
Formula
(repeating unit)
Na15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3
(Si3O9)2(Si9O27)2(OH,Cl)2
Strunz classification9.CO.10
Crystal systemTrigonal
Crystal classHexagonal scalenohedral (3m)
H-M symbol: (3 2/m)
Space groupR3m
Unit cella = 14.31, c = 30.15 [Å]; Z = 12
Identification
ColorRed, magenta, brown; also blue and yellow
Crystal habitCrystals short rhombohedral to long prismatic, granular, irregular masses
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.svg Radioactive
References[1][2][3]
Pink Eudialyte in syenite (lujavrite) from Poços de Caldas, Brazil. The white mineral is alkali feldspar, the black is aegirine, and the little brown bits are biotite.

Eudialyte was first described in 1819 for an occurrence in nepheline syenite of the Ilimaussaq intrusive complex of southwest Greenland.[1]

Uses of eudialyteEdit

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, geoscientists use eudialyte as a geochronometer to date and investigate the genesis of the host rocks.[4]

Associated mineralsEdit

Eudialyte is found associated with other alkalic igneous minerals, in addition to 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 namesEdit

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 identificationEdit

Eudialyte's rarity makes locality useful in its identification. Prominent localities of eudialyte include Mont Saint-Hilaire in Canada, Kola Peninsula in Russia and Poços de Caldas in Brazil, 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 groupEdit

Microchemical (by electron microprobe) and structural analyses of different eudialyte (and related) samples have revealed the presence of many new eudialyte-like minerals. These minerals are structurally and chemically related and joined into the 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.

ReferencesEdit

  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. (April 2010). "In situ U-Pb, Sr, Nd and Hf isotopic analysis of eudialyte by LA-(MC)-ICP-MS". Chemical Geology. 273 (1–2): 8–34. Bibcode:2010ChGeo.273....8W. doi:10.1016/j.chemgeo.2010.02.007.
  5. ^ Eucolite on Mindat

Further readingEdit

  • Johnsen, O.; Ferraris, G.; Gault, R.A.; Grice, D.G.; Kampf, A.R.; Pekov, I.V. (June 2003). "The nomenclature of eudialyte-group minerals". The Canadian Mineralogist. 41 (3): 785–794. doi:10.2113/gscanmin.41.3.785.