EmeraldFrom Wikipedia, the free encyclopediaFor other uses, see Emerald (disambiguation).EmeraldEmerald crystal muzo colombia.jpgEmerald crystal from Muzo, ColombiaGeneralCategory Beryl varietyFormula(repeating unit) Be3Al2(SiO3)6Crystal symmetry (6/m 2/m 2/m) – Dihexagonal DipyramidalUnit cell a = 9.21 Å, c = 9.19 Å; Z = 2IdentificationFormula mass 537.50Color Green shades to colorlessCrystal habit Massive to well CrystallineCrystal system Hexagonal (6/m 2/m 2/m) Space group: P6/mсcCleavage Imperfect on the [0001]Fracture ConchoidalMohs scale hardness 7.5–8Luster VitreousStreak WhiteDiaphaneity Transparent to opaqueSpecific gravity Average 2.76Optical properties Uniaxial (-)Refractive index nω = 1.564–1.595,nε = 1.568–1.602Birefringence δ = 0.0040–0.0070Ultraviolet fluorescence None (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 10-point Mohs scale of mineral hardness.[2] Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.Contents [hide]1 Etymology2 Properties determining value2.1 Color2.2 Clarity2.3 Treatments3 Emerald localities4 Synthetic emerald5 Emerald in different cultures, and emerald lore6 Notable emeralds7 Gallery8 See also9 References10 Further reading11 External linksEtymology[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 originated in Greek: σμάραγδος (smaragdos; "green gem").[3]Properties determining value[edit]Cut emeraldsEmeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of Connoisseurship: Color, Cut, Clarity and Carat weight. Before the 20th century, jewelers used the term water, as in "a gem of the finest water",[4] to express the combination of two qualities: color and clarity. Normally, in the grading of colored gemstones, color is by far the most important criterion. However, in the grading of emeralds, crystal is considered a close second. Both are necessary conditions. A fine emerald must possess not only a pure verdant green hue as described below, but also a high degree of transparency to be considered a top gem.[5]In the 1960s, the American jewelry industry changed the definition of "emerald" to include the green vanadium-bearing beryl as emerald. As a result, vanadium emeralds purchased as emeralds in the United States are not recognized as such in the UK and Europe. In America, the distinction between traditional emeralds and the new vanadium kind is often reflected in the use of terms such as "Colombian Emerald".[6]Color[edit]In gemology,[citation needed] color is divided into three components: hue, saturation and tone.[7] Emeralds occur in hues ranging from yellow-green to blue-green, with the primary hue necessarily being green. Yellow and blue are the normal secondary hues found in emeralds. Only gems that are medium to dark in tone are considered emerald; light-toned gems are known instead by the species name green beryl. The finest emerald are approximately 75% tone on a scale where 0% tone would be colorless and 100% would be opaque black. In addition, a fine stone should be well saturated; the hue of an emerald should be bright (vivid). Gray is the normal saturation modifier or mask found in emerald; a grayish-green hue is a dull green hue.[5]Emeralds are green by definition (the name is derived from the Greek word "smaragdus", meaning green).[8] Emeralds are the green variety of beryl, a mineral which comes in many other colors that are sometimes also used as gems, such as blue aquamarine, yellow heliodor, pink morganite, red red beryl or bixbite, not to be
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