Emerald
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 much material trapped inside during the gem's formation,[3] so their toughness (resistance to breakage) is classified as generally poor. Emerald is a cyclosilicate.
For other uses, see Emerald (disambiguation).Emerald
Beryl variety
Be3Al2(SiO3)6
Hexagonal (6/m 2/m 2/m) Space group: P6/mсc
(6/m 2/m 2/m) – dihexagonal dipyramidal
a = 9.21 Å, c = 9.19 Å; Z = 2
537.50
Bluish green to green
Massive to well Crystalline
Imperfect on the [0001]
7.5–8
White
Transparent to opaque
Average 2.76
Uniaxial (−)
nω = 1.564–1.595,
nε = 1.568–1.602
δ = 0.0040–0.0070
None (some fracture-filling materials used to improve emerald's clarity do fluoresce, but the stone itself does not)
Etymology[edit]
The word "emerald" is derived (via Old French: esmeraude and Middle English: emeraude), from Vulgar Latin: esmaralda/esmaraldus, a variant of Latin smaragdus, which was via Ancient Greek: σμάραγδος (smáragdos; "green gem") from a Semitic language.[4] According to Webster's Dictionary the term emerald was first used in the 14th century.[5]
Emerald on quartz, from Carnaiba Mine, Pindobaçu, Campo Formoso ultramafic complex, Bahia, Brazil
The Chalk Emerald ring, containing a top-quality 37-carat emerald, in the U.S. National Museum of Natural History
Emerald crystals
Gachalá Emerald, one of the largest gem emeralds in the world, at 858 carats (171.6 g). Found in 1967 at La Vega de San Juan mine in Gachalá, Colombia. Housed at the National Museum of Natural History in Washington, D.C.
Rough emerald crystals from Panjshir Valley Afghanistan
Large, di-hexagonal prismatic crystal of 1,390 carats uncut with a deep green color. It is transparent and features few inclusions in the upper 2/3, and is translucent in the lower part. Housed at the Mim Museum, Beirut, Lebanon.
