Emerald

Emerald
Emerald crystal from Muzo, Colombia
General
CategoryBeryl variety
Formula
(repeating unit)
Be3Al2(SiO3)6
Crystal systemHexagonal (6/m 2/m 2/m) Space group: P6/mсc
Space group(6/m 2/m 2/m) – dihexagonal dipyramidal
Unit cella = 9.21 Å, c = 9.19 Å; Z = 2
Identification
Formula mass537.50
ColorBluish green to green
Crystal habitMassive to well Crystalline
CleavageImperfect on the [0001]
FractureConchoidal
Mohs scale hardness7.5–8
LusterVitreous
StreakWhite
DiaphaneityTransparent to opaque
Specific gravityAverage 2.76
Optical propertiesUniaxial (−)
Refractive indexnω = 1.564–1.595,
nε = 1.568–1.602
Birefringenceδ = 0.0040–0.0070
Ultraviolet fluorescenceNone (some fracture-filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)
References[1]
Main emerald producing countries

Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium or sometimes vanadium.[2] Beryl has a hardness of 7.5–8 on the Mohs scale.[2] Most emeralds have many inclusions,[3] so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.

  1. ^ Cite error: The named reference Mindat was invoked but never defined (see the help page).
  2. ^ a b Hurlbut, Cornelius S. Jr., and Kammerling, Robert C. (1991). Gemology, John Wiley & Sons, New York, p. 203, ISBN 0-471-52667-3.
  3. ^ "Emerald Quality Factors". Gemological Institute of America. Archived from the original on 2 November 2016. Retrieved 1 November 2016.

Emerald

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