Difference between revisions of "Phenakite"

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[[Image:Phenakitetv6.jpg|thumb|left|240px|A facetted colorless gem quality phenakite.<br />Photo courtesy of Chaman Golecha, Gem Testing Laboratory, Jaipur]]
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Geological Occurrence: Commonly n pegmatites, mica schists, in granite drusses
 
Geological Occurrence: Commonly n pegmatites, mica schists, in granite drusses
  

Revision as of 03:52, 23 August 2007

A facetted colorless gem quality phenakite.
Photo courtesy of Chaman Golecha, Gem Testing Laboratory, Jaipur


Geological Occurrence: Commonly n pegmatites, mica schists, in granite drusses

Geographical Locations: Tokajawa river, Ural Mountains with emerald and chrysoberyl; Miask district, Rissia; large colourless crystals at San Miguel di Praciavaba, Minas Gerais; Tanzania; Maine, New Hampshire & Colarado, USA; Switzerland; Austria; Alsace, France; Namibia; Norway and Sri Lanka (large stone)

Crystallography: Trigonal system; Tabular, prismatic, rhombohedral, acicular.

Composition: Beryllium Silicate ( Be2SiO4)

Colour Varieties: Colourless; also yellow, pink, brown, pinkish red due to surface stains.

Physical Properties: Hardness: 7.5-8; S.G. 2.92-2.97; Cleavage: Indistinct one direction; Fracture: Conchoidal; brittle stone.

Optical Properties: Transparent; Luster: Vitreous; Optic Character: DR, Uniaxial Positive R.I.: o:1.651-1.654 and e:1.663-1.670; D.R.: 0.016 Dispersion: Low Spectrum: Not charecteristic UV fluorescence: Sometimes pale greenish / blue or pale rose and under X-rays is blue Pleochroism: Seen in strongly coloured stones

Inclusions: May have many needle inclusions; 2-phase; fingerprints with phase inclusions.

Simulants: Spodumene: Magnification features, UV, Biaxial figure, cleavage and S.G Sillimanite: S.G, R.I, Birefringence, Biaxial Figure Rock Crystal: Lower S.G (floats 2.88), Bulls eye optic figure, R.I etc. Topaz: More heft (sinks 3.33), Biaxial figure, R.I etc.