EMERALD

A silicate of aluminium and beryllium which is green in colour due to the presence of chromium and vanadium. It is a green variety of beryl and may sometimes be confused with amazonite, quartz or green chalcedony. It has a glassy appearance and is often brittle and easily cracked. Perfect specimens are rare and very valuable. Most samples are flawed and cloudy and the colour is often distributed irregularly across the face. For this reason emeralds are sometimes filled with oil to disguise imperfections. They may also be cut in a specific way to hide flaws. A special cut has been devised which accentuates it's finest qualities.

It is fairly hard (7.5-8 on the mohs scale) and is in high demand for jewellery. There are many synthetic emeralds on the market which are often made from glass.

In ancient times it was considered to be useful for healing. Some even believed it had the power to restore sight.

It forms in granites and pegmatites and can be found in open-cast mines in some metamorphic rocks.

The best emeralds come from mines in Columbia. They were discovered here in 1537 during the Spanish invasion. Emeralds may also be found in South Africa, Russia, Brazil, Pakistan, Zambia and Zimbabwe. Russian emeralds always contain mica and nearly all Brazilian emeralds contain calcite or pyrite

The greatest collection of emeralds can be found stored in the Republic of Bogota Bank in Columbia. There are also beautiful specimens at the Topkapi museum in Istanbul, Turkey.

EPIDOTE

A silicate which contains calcium, aluminium, iron, silica, oxygen and hydrogen (some metals may be replaced by magnesium or manganese). When it contains manganese it is known as withamite. Epidote can be yellow, green or black.

It forms in unusual crystal shapes. It's crystals have four sides with two being longer than the other two. Other minerals and gemstones with a similar make-up are said to belong to the epidote group. One such mineral is zoisite. This is the most widespread member of the epidote group. Thulite is a form of zoisite and is pink due to the presence of manganese. Another form of zoisite is tanzanite, which is blue or purple and derives it's name from where it was discovered (Tanzania).

It is moderately hard (6-7 on the mohs scale) and only some specimens of epidote are classified as gemstone quality.

It occurs in sedimentary, igneous and metamorphic rocks.

It can be found in Saltzburg (Austria), Brazil, Japan, Madagascar, Russia and Alaska.