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Eudialyte

Cyclosilicate mineral


Cyclosilicate mineral

FieldValue
nameEudialyte
categoryCyclosilicate
imageEudialyte-163974.jpg
imagesize290px
formulaNa15Ca6(Fe,Mn)3Zr3SiO(O,OH,H2O)3
(Si3O9)2(Si9O27)2(OH,Cl)2
IMAsymbolEud
strunz9.CO.10
systemTrigonal
classHexagonal scalenohedral (m)
H-M symbol: ( 2/m)
symmetry*R*m
unit cella = 14.31, c = 30.15 [Å]; Z = 12
colorRed, magenta, brown; also blue and yellow
habitCrystals short rhombohedral to long prismatic, granular, irregular masses
cleavageDistinct on {0001} imperfect on {110}
fractureUneven
tenacityBrittle
mohs5–6
lusterVitreous
refractivenω = 1.606–1.610 nε = 1.610–1.613
opticalpropUniaxial (+/−)
birefringenceδ = 0.004
pleochroismWeak: O= colorless, pale yellow, pink; E= pink to colorless
streakWhite
gravity2.74–3.10
solubilityH2SO4
diaphaneityTransparent to translucent
otherMildly [[Image:Radioactive.svg25px]] Radioactive
references

(Si3O9)2(Si9O27)2(OH,Cl)2 H-M symbol: ( 2/m)

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.

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

Uses

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.

Associated minerals

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.

Alternative names

Alternative names of eudialyte include: almandine spar, eudalite, Saami blood.

Notes for identification

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. Iron (Fe2+) provides the color.

Eudialyte group

Main article: Eudialyte group

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.

References

References

  1. Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
  2. [http://www.mindat.org/min-1420.html Eudialyte on Mindat.org]
  3. [http://rruff.geo.arizona.edu/doclib/hom/eudialyte.pdf Handbook of Mineralogy]
  4. [http://www.webmineral.com/data/Eudialyte.shtml Eudialyte on Webmineral]
  5. (April 2010). "''In situ'' U-Pb, Sr, Nd and Hf isotopic analysis of eudialyte by LA-(MC)-ICP-MS". Chemical Geology.
  6. Eucolite is the name of an optically negative variety, more accurately the group member: [[ferrokentbrooksite]].[http://www.mindat.org/min-9184.html Eucolite on Mindat]
  7. "Minerals Colored by Metal Ions".
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