In the 19th century the preferred colour for aquamarine was sea-green, and indeed the name itself means sea water. Today, the most valued colours are sky-blue and dark blue. Aquamarine is dichroic, appearing blue or colourless as the stone is viewed from different angles. Gem-quality aquamarine is found as hexagonal crystals, which may be up to 1m long and flawless, with striations along the length of the crystal. Aquamarine is often cut with the table facet parallel to the length of the crystal in order to emphasize the deepest coloration. The best of the gem-quality aquamarine is found in Brazil, where it occurs in pegmatites and alluvial deposits of gravel, locally called cascalho. Other localities include the Urals (Russia), Afghanistan, Pakistan, India and more recently exploited, Nigeria. A dark blue variety occurs in Madagascar. Almost all aquamarine in the market has been heat-treated to enhance its colour. Care must be taken not to overheat the stones, as they may become colourless.
Emerald derives its beautiful green colour from the presence of chromium and vanadium. Emeralds are rarely flawless, so stones are often oiled to fill and disguise cracks, hide flaws, and enhance colour. To minimize the loss of material, the step-cut (or “emerald-cut”, as it is known) is commonly used, but ancient engravings are known, and cameos, intaglios, and beads can make the best of a flawed stone. Found in granites, pegmatites, and schists, as well as alluvial deposits, the finest emeralds are from Colombia. Other sources are Austria, India, Australia, Brazil, South Africa, Egypt, the USA, Norway, Pakistan and Zimbabwe. Most emeralds used in historical jewellery would have been from Cleopatra’s mines in Egypt, which now yield only poor-quality emeralds.
Goshenite is the pure, colourless variety of beryl. It has been used to imitate diamond or emerald, by placing silver or green-coloured metal foil behind a cut goshenite gemstone, then placing the stone in a closed setting so that the foil cannot be detected. Goshenite is named after Goshen, Massachusetts, in the USA, where it was first found. Present localities include Canada, Brazil and the former USSR. Pale and colourless beryl was once used for the lenses in spectacles, thus the German word for spectacles, brille, may have been derived from the word “beryl”.
Heliodor, a yellow or golden yellow form of beryl, has always been linked with the Sun. Gem-quality specimens are occasionally found, but more usually inclusions of fine, slender tubes are present which are visible to the naked eye. Heliodor is found associated with aquamarine in granitic pegmatites. The best-quality stones are found in the Urals (Russia). Brazilian heliodor is often a pale yellow and is step-cut to give depth of colour. Heliodor from Madagascar is a finer colour. Other localities include the Ukraine, Namibia, and the USA.
Coloured by manganese impurities, the pink, rose, peach and violet varieties of beryl are called morganite after the American banker and gem enthusiast, J. Pierpoint Morgan. Morganite tends to occur as short and stubby (tabular) prisms and is dichroic showing either two shades of the body colour, or one shade and colourless. The first morganite to be described was a pale rose-coloured specimen from California (USA), where it occurred with tourmaline. Some of the finest morganite is from Madagascar; Brazil produces pure pink crystals, as well as some containing aquamarine and morganite in the same crystal. Other localities include Elba (Italy), Mozambique, Namibia, Zimbabwe and Pakistan (recently discovered). Stones with a yellow or orange tinge may be heat-treated for a purer pink.
Very rare and seldom seen as a cut stone, red beryl nonetheless has an unusually intense colour due to the presence of manganese. Found in rhyolites in the Thomas Mountains and Wah Wah Mountains in Utah in the USA. Red beryl is also called bixbite (not to be confused with bixbyite, a manganese-iron oxide).
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