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Emerald

Emerald is a variety of the mineral beryl, colored green by trace amounts of chromium varying of a blue hue of color. The Russian name "emerald" is derived from the Turkish name of this stone "zümrüt", distorted during the times from the Semitic root "shine" (for example, the closest in sounding in Hebrew "בָּרֶקֶת" - "bareket" and in Sanskrit "मरकत" "Marakata" is an "emerald").

Chemistry: Ве₃А1₂[Si₆O₁₈];

Crystal system: Hexagonal, dihexagonal-dipyramidal crystal class (point symmetry group);

Color: Green, bluish green.

The Al₆³⁺ isomorphic substitution for Cr₆³⁺. is cause of green color. Additional shades are caused by the occurrence as an isomorphous impurity of the V₆³⁺ and Fe₄³⁺ ions (in the ionically bound [O^2- – Fe₄³⁺]), as well as Fe₆²⁺ and Fe₄²⁺ ions. Sometimes the influence of the Fe₆³⁺, Mn₆³⁺, Ti₆³⁺, as well as Mg₆²⁺, Ca₆²⁺ ions of other metals affect the color of the emerald.

Identification properties

Physical properties
Mohs hardness:	7.5-8
Density:	2.6 – 2.9 g/cm³
Cleavage:	imperfect
Fracture:	conchoidal

Optical properties
Optical character:	anisotropic, uniaxial , negative Sometimes anomalously biaxial (refers to twins, and distorted crystals)
Refractive Index:	n_o = 1.567-1.604, n_е = 1.561-1.596
Birefringence:	0.005 – 0.009
Pleochroism:	Green shades to colorless
Dispertion:	0.014 (BG)
Luster:	vitreous

Inclusions and structural inhomogeneities

Two- and three-phase inclusions

Mineral inclusions

Gem basic treatments

Treatment	Goal
Healing of fractures (cracks) or even filling surface-reaching fractures or cavities with fillers with a refractive index close to that of emerald (oils, waxes, polymers)	Improving the apparent clarity of gem material
Tinting of the surface or filler material of open cavities	Enhancing the color properties
Irradiation treatment	Altering the gem visual color
Surface coating by applying a various coloring agent	Altering the gem visual color

Techniques for color enhancing by the "ion implantation" technique, complex ennobling by hydrothermal build-up of the surface layer of a synthetic emerald, as well as the technique of filling fractures with mineral compounds are described in the literature.

Inclusions and structural inhomogeneities

Filling cracks with colored agents

Filling cracks with colorless agents

Synthetic or Imitation gem materials

Synthetic emerald for the jewelry industry is produced by several synthetic methods based on the principle of temperature gradient. This is a group of growing methods in an aqueous solution and a group of methods for growing from a solution in a melt (flux-growth methods).

The most commonly encountered synthetic emerald is as follows:

pale green beryl irradiation treated;
beryl colored in emerald color from the surface or over open cavities;
beryl treated by "ion impregnation" - very rarely;
beryl, a layer of synthetic emerald treated;
doublets: emerald + beryl, green garnet + beryl; beryl + glass;
natural minerals with similar color properties: actinolite-smaragdite; chrome-vesuvian, rarely grossular-tsavorite, chrome-diopside, green tourmaline (chrome-tourmaline and verdelite);
beryl glasses;
color glasses.