COPAL

An organic substance with a variable chemical composition which is mainly yellow but may also be orange. It has no crystal structure and is therefore amorphous and has no chemical formula. It has a greasy sheen and is buoyant. It is very soft (2-2.5 on the mohs scale) which limits it's use as jewellery.

Copal is derived from solidified resins which are secreted by particular species of tropical trees (Brazilian Copal). There are two varieties, Trachylobium verrucosum (mainly found in East Africa) and Hymenaea Courbaril (usually found in South American jungles). It may also be extracted in liquid form from the roots of living trees. It can be found today on land in fossilised form. The forests from which it originates no longer exist.

It is very similar to amber the only difference being the trees from which they are derived. Amber forms from conifers in temperate climates whereas copal only forms in the tropics.

It may be found in Brazil, Columbia, Kenya, Madagascar, Tanzania and Zaire.

CORAL

Coral is composed of the skeletal remains of sea creatures (coral polyps). It has a variable chemical composition and therefore has no formula although most specimens are almost entirely composed of calcium carbonate.

The most valuable specimens are dull in colour when first removed from the sea and develop a glassy sheen when polished. It's softness (3 on the mohs scale), sensitivity to heat and tendency to fade limit it's use as a gemstone.

There are 2 main varieties, one which can be blue/pink/red/white and is composed mainly of calcium carbonate. The other is black/gold and is formed from a substance called conchiolin which forms the basic structure of all sea shells. Red specimens are the most valuable but the rarest is blue coral.

Most coral species live in large groups. Coral grows by extracting dissolved carbonate salts from the surrounding water and converting them into a hard shell made up of calcium carbonate. They grow on top of each other and develop into reefs or atolls.

Coral can only exist in water warmer than 22 degrees centigrade. Therefore it can mostly be found in shallow tropical waters 30 degrees S to 30 degrees N of the equator. The most popular red coral is found around the coasts of Japan and Africa. The black/gold variety can be found off the coast of Australia, in the Caribbean Sea, the Indian Ocean and off the coast of Hawaii. The blue coral can be found off the west coast of Cameroon.