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Emerald

Octagonal Step Cut Emerald

Properties
Chemical Composition: 
Beryllium Aluminium Silicate (Be3Al2(SiO3)6; Trace elements are Cr, V, Fe, Mn, etc.
Classification / Type: 
-
Colors / Varieties: 
Green (Cr/V/Fe)
  • Trapiche emerald - green with black spokes intersecting.
Crystal System / Forms: 
Hexagonal System
Hardness: 
7.5 - 8
Specific Gravity: 
2.68 - 2.80
Cleavage / Fracture: 
Poor cleavage / parting parallel to the basal plane. Emerald is a brittle stone.
Optic Character: 
Anisotropic, D.R.; Uniaxial Negative.
Lustre: 
Vitreous.
Refractive Index / Birefringence: 
1.577 - 1.583 / 0.006 - 0.009. R.I. Range: 1.57 - 1.60
Pleochroism: 
Distinct dichroism depending on depth of color.
Dispersion: 
0.014
Magnification: 
  • Columbian Emerald from Columbia (Muzo, Chivor): Jagged three-phase, two phase and other fluid inclusions. Crystals (pyrite - Chivor, calcite - Muzo). Six black spokes of carbonaceous material in Trapiche emeralds.
  • Transvaal (Cobra Mine): Crystals (molybdenite, biotite), fluid and phase inclusions.
  • Tanzania (Lake Manyara): Crystals (orthoclase, biotite, quartz), fluid and phase inclusions.
  • Pakistan (Swat Valley): Growth tubes, negative crystals, fluid, phase and crystal (dolomite) inclusions.
  • Brazil: Parallel growth tubes, crystal inclusions (biotite, chromite, pyrite, dolomite).
  • Zimbabwe (Sandwana): Curved tremolite fibers, garnet crystals with a yellow halo, fluid and phase inclusions.
  • India (Rajasthan): Parallel rectangular two phase inclusions, crystal inclusions (biotite).
  • Zambia (Kitwe, Kafubu, Miku): Crystal inclusions (magnetite, rutile, muscovite, hematite), limonite filled tubes, phase and fluid inclusions.
  • U.S.S.R. (Ural Mountains): Actinolite blades, biotite flakes, fluid, phase and crystal inclusions.
U.V. Fluorescence: 
Variable.
Spectrum: 
Strong lines at 685nm, 680nm, 640nm, band at center 600nm, lines at 477.5nm and 472.5nm
Cause of Color: 
Cr and / or V, with varying amounts of Iron.
Treatment (Enhancement): 
Specific Tests & Remarks: 
Emerald is brittle and may crack when exposed to heat.
Synthesis: 
Flux fusion and hydrothermal method, emerald overgrowth by hydrothermal method
Simulants (with key separation tests): 
Synthetic emerald (inclusions), glass (optic character, inclusions), fluorite (optic character, U.V. fluorescence, R.I., S.G.), apatite (R.I., S.G., spectrum), dioptase (R.I., S.G., cleavage), aventurine quartz (structure, inclusions, R.I.), composite (inclusions, spectrum).
Geological Occurrence: 
Granitic rocks - pegmatite and schists, in hydrothermal veins and metamorphic limestone.
Sources: 
South America (Columbia; Brazil), Africa (Zambia; Nigeria; Zimbabwe; Tanzania; Transvaal; Mozambique; Madagascar), Pakistan (Swat), Afghanistan (Pancher), India (Rajasthan, Orissa), Russia (Ural Mountains), Austria (Habachtal), Australia
Cuts & Uses: 
Facetted cuts, cabochons, beads, carvings, etc.
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