Emerald Beryl

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.

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): 

• Colorless impregnation: oil / resin to improve clarity
• Colored impregnation: dyes / resin to improve clarity and color

Specific Tests & Remarks: Emerald is brittle and may crack when exposed to heat.

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: Emrald cut, Facetted cuts, cabochons, beads, carvings, etc.