Emerald

emerald
Colombian Emerald

Emerald derives its beautiful green colour from the presence of chromium and vanadium. Emeralds are rarely flawless, so stones are often oiled to fill and disguise cracks, hide flaws, and enhance colour. To minimize the loss of material, the step-cut (or “emerald-cut”, as it is known) is commonly used, but ancient engravings are known, and cameos, intaglios, and beads can make the best of a flawed stone.

Found in granites, pegmatites, and schists, as well as alluvial deposits, the finest emeralds are from Colombia. Other sources are Austria, India, Australia, Brazil, South Africa, Egypt, the USA, Norway, Pakistan and Zimbabwe.

Most emeralds used in historical jewellery would have been from Cleopatra’s mines in Egypt, which now yield only poor-quality emeralds.

Emerald Pictures

Rough emeralds from Brazil Looose step-cut emeralds Beautiful emerald necklace with diamondsEmerald in hexagonal form Emerald Ring

Cause of Color :

Cr and / or V, with varying amounts of Iron.

Chemical Composition :

Beryllium Aluminium Silicate (Be3Al2(SiO3)6; Trace elements are Cr, V, Fe, Mn, etc.

Crystal System / Forms :

Hexagonal System

Cuts & Uses :

Facetted cuts, cabochons, beads, carvings, etc.

Dispersion : 0.014
Hardness : 7.5 - 8
Lustre : Vitreous.
Magnification :
  • Colombian Emerald from Colombia (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.
Optic Character :

Anisotropic, D.R.; Uniaxial Negative.

Pleochroism : Distinct dichroism depending on depth of color.
Refractive Index / Birefringence :

1.577 – 1.583 / 0.006 – 0.009. R.I. Range: 1.57 – 1.60

Simulants (with 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).

Sources :

South America (Colombia; Brazil), Africa (Zambia; Nigeria; Zimbabwe; Tanzania; Transvaal; Mozambique; Madagascar), Pakistan (Swat), Afghanistan (Pancher), India (Rajasthan, Orissa), Russia (Ural Mountains), Austria (Habachtal), Australia

Specific Tests :

Emerald is brittle and may crack when exposed to heat.

Spectrum :

Strong lines at 685nm, 680nm, 640nm, band at center 600nm, lines at 477.5nm and 472.5nm

Synthesis :

Flux fusion and hydrothermal method, emerald overgrowth by hydrothermal method

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