Emerald

Emerald
Béryl var. émeraude sur gangue (Muzo Mine Boyaca - Colombie) 2.jpg
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
ColorGreen shades to colorless
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]

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

Etymology

The word "emerald" is derived (via Old French: esmeraude and Middle English: emeraude), from Vulgar Latin: esmaralda/esmaraldus, a variant of Latin smaragdus, which originated in Ancient Greek: σμάραγδος (smaragdos; "green gem").[4]