Emerald is a mineral with a hardness of 8 out of 10 on the Mohs scale of mineral hardness [?]. These Hexagonally structured gems are made of silicate, their full chemical compound being Be3Al2(SiO3)6.
Emerald is the most prized variety of the mineral Beryl. It sometimes fetches higher prices than diamond. It appears as pale green to bright green.
Though it is the green variety of beryl, not all gem-quality green beryls are called emeralds; yellow-green stones are called "heliodors;"soft blue-green or even pale green specimens are called "aquamarines."
The typical color of emerald is a beautiful, distinct hue known as "emerald green" and is due to traces of chromium, sometimes vanadium, in the crystal structure. Emeralds can be light or dark green, bright green or leaf-green. The color is very stable against light and heat, and only alters at 700-800 C.
All emeralds are brittle and combined with internal stresses, are sensitive to pressure; care must be taken in heating them. They are resistant to chemicals with the exception of fluoric acid.
The emerald color is virtually unmistakable, only equalled by some very rare specimens of jadeite jade which is less transparent and has different physical properties.
All emeralds contain inclusions, although in the best quality stones, these are very faint and not visible to the naked eye. The vitreous luster is not outstanding, and is strongest in medium-light stones with few inclusions.
Inclusions in emerald can be highly distinctive: a bubble of gas in a liquid, within spindle-shaped, or more rarely, truncated, prismatic cavities; birefringent, circular plates of mica; multifaceted pyrite crystals or calcite rhombohedra. But a microscope is almost always needed to recognize them. These are not classified as faults, but are evidence as to the genuineness of the stone as compared with synthetic and other imitations. Experts refer to these inclusions as "jardin."
The biggest and most beautiful emeralds come from the Chivor and Muzo mines of Colombia. Mined by the Incas, the Muzo deposit was abandoned, then rediscovered in the 17th century. The mine yields fine quality stones of a deep green color.
Much smaller quantities of emeralds, mostly of medium-light color, come from Brazil, and small, very intensely colored stones are found in the Transvaal (South Africa).
Quantities of emeralds have been found in a series of small deposits in Zimbabwe, Zambia, and Tanzania. These sometimes have a bluish green tinge, often contain mica plates, and thin crystal needles. The most famous are the ones from Sandawana in Zimbabwe, which are valued for their color. Emeralds with similar characteristics also come from the mountains of India and Pakistan, as well as the Soviet republics, and Austria.
Stones of fine color, weighing more than 2 carats, are among the most highly valued gemstones. Less ideally colored varieties too dark or too pale are worth quite a lot less.
The most common shape for gems is the step or trap cut, also known as the emerald cut. Because emerald is so sensitive to knocks, the emerald cut was developed, the four corners being truncated by facets. They are occasionally given a mixed, oval cut, while antique stones are found with hexagonal, step cuts, cabochon cuts, or pear-shapes with a hole in them, often used as pendants. Turbid stones are only used for cabochons or as beads for necklaces.
There are many well-known large emeralds, as famous as diamonds and rubies. Some beautiful specimens of several carats are kept by the British Museum of Natural History (London, England), by the American Museum of Natural History (New York, USA), in the treasury of Russia and in the Persian crown jewels. In the Viennese treasury is a jug weighing 2205 carats, cut from a single emerald crystal.
Other stones are mistaken for emerald, such as demantoid, diopside, dioptase, grossular, hiddenite, peridot, green tourmaline, and uvarovite.
The name is of ancient origin. The Latin "smaragdus" (which derives from Persian) which means "green stone" appears to have referred to all green stones, as well asthe stone we call emerald, which is now considered as a distinct species.
Emeralds are formed by rising magma and metamorphism. Deposits are therefore found mainly in or near pegmatite veins. Mining is nearly exclusively from host rock, where the emerald has grown into small veins or in walls of cavities. The host rock is black, carbonaceous limestone. Accompanying minerals are albite, apatite, aragonite, barite, calcite, dolomite, fluorite, and pyrite.
Emerald was mined in Upper Egypt in about 2000 BC. Queen Cleopatra is supposed to have owned an emerald on which her portrait was engraved. The short-sighted emperor Nero may have used an emerald as a monocle, but historians now think that it was probably made of the pale blue variety aquamarine.
The Romans are known to have imitated emerald with skilfully worked green glass. Glass was also used in later centuries, extraneous particles sometimes being incorporated to simulate inclusions.
Doublets have also been used as imitations, with a lower portion of green glass and a top portion of garnet, or triplets, with a layer of colored cement sandwiched between two layers of colorless beryl, synthetic spinel, or quartz.
The first emerald synthesis was made in 1848 by a Frenchman. Since the turn of the century various methods have been developed and, since the 1950s, commercial products of excellent quality have appeared on the market.
Synthetic emeralds are now widely produced. Generally of good color, they are mainly distinguished from the natural variety by their inclusions and other growth features. Synthetic emerald transmits short ultraviolet light more than natural emerald. There are also stones with synthetic emerald "plating" on colorless beryl, as well as glass imitations.