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Emerald

Emerald

One of the four precious stones, the emerald is a variety of the mineral beryl and owes its green colour to traces of the elements chromium and, sometimes, vanadium. Beryl scores 7.5-8 on the Mohs scale of mineral hardness (on which diamonds score 10). However, most emeralds are ‘heavily included’. An inclusion in a gem is anything that interferes with the passage of light, these may be minerals, for example. Because of this, the resistance to breakage of emeralds is classified as poor.

Richblu’s emeralds are mined in Brazil, Columbia and Zambia.

General

Category

Beryl variety

Formula

Be3Al2(SiO3)6

(repeating unit)

Crystal symmetry

(6/m 2/m 2/m) – DihexagonalDipyramidal

Unit cell

a = 9.21 Å, c = 9.19 Å; Z = 2

Identification

Formula mass

537.5

Color

Green shades to colorless

Crystal habit

Massive to well Crystalline

Crystal system

Hexagonal (6/m 2/m 2/m) Space group: P6/mсc

Cleavage

Imperfect on the [0001]

Fracture

Conchoidal

Mohs scale hardness

7.5–8

Luster

Vitreous

Streak

White

Diaphaneity

Transparent to opaque

Specific gravity

Average 2.76

Optical properties

Uniaxial (-)

Refractive index

nω = 1.564–1.595,

nε = 1.568–1.602

Birefringence

δ = 0.0040–0.0070

Ultraviolet fluorescence

None (some fracture filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)