Emerald Emeralds are fascinating gemstones. They have the most beautiful, most intense and most radiant green that can possibly be imagined: emerald green. Inclusions are tolerated. In top quality, fine emeralds are even more valuable than diamonds
Emerald is a gemstone and a variety of the mineral beryl (Be3Al2(SiO3)6) colored green by trace amounts of chromium and sometimes vanadium. Beryl has a hardness of 7.5–8 on the Mohs scale. Most emeralds are highly included, so their toughness (resistance to breakage) is classified as generally poor.
Emeralds, like all colored gemstones, are graded using four basic parameters–the four Cs of Connoisseurship: Color, Cut, Clarity and Carat weight.
In gemology,color is divided into three components: hue, saturation and tone. 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.
Emeralds are green by definition (the name is derived from the Greek word “smaragdus”, meaning green).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 beryl or bixbite, not to be confused with bixbyite, and colorless goshenite.
Emerald tends to have numerous inclusions and surface breaking fissures. Unlike diamond, where the loupe standard, i.e. 10× magnification, is used to grade clarity, emerald is graded by eye. Thus, if an emerald has no visible inclusions to the eye (assuming normal visual acuity) it is considered flawless. Stones that lack surface breaking fissures are extremely rare and therefore almost all emeralds are treated (“oiled”, see below) to enhance the apparent clarity.
Faceted Emeralds are most commonly given the Oval cut, or the signature Emerald cut, a rectangular cut with facets around the top edge.
Some of the most rare emeralds come from three main emerald mining areas in Colombia: Muzo, Coscuez, and Chivor. Fine emeralds are also found in other countries, such as Zambia, Brazil, Zimbabwe, Madagascar, Pakistan, India, Afghanistan and Russia.
Stone Family: Beryl
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  Fracture: Conchoidal
Mohs scale hardness: 7.5–8
Diaphaneity: Transparent to opaque
Specific gravity: Average 2.76
Optical properties: Uni-axial (-)
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)