GEMS DERIVED FROM ANIMALS AND PLANTS are described as organic. They include amber, jet, coral, pearl, and shell. They are not as hard (4 or less) or as dense (1.04 amber to 2.78 pearl) as gemstones but have been popular for thousands of years because of their beauty. Beads of shell and amber have been found in ancient graves dating from 2000 B.C. Pearls have long been symbols of beauty and purity and greatly valued. The Roman emperor Julius Caesar is said to have paid the equivalent of about £150,000 ($350,000) for a single pearl.
Jet and amber
Jet and amber both come from trees. Jet is a fine-grained, black rock formed over millions of years from rotted and compressed trees, in a similar way to coal. Amber is the fossilized resin, or sap, of trees that lived as much as 300 million years ago.
Coral is a skeleton of calcium carbonate made by colonies of soft-bodied animals which live in tropical or sub-tropical waters. The range of colours, from black to blue to cream to red, is due to different growth conditions and organic contents.
Pearl and shell
The sheen on pearls and the inside of some shells is caused by light reflecting on tiny platelets of calcium carbonate called nacre. Pearls, found in some marine and freshwater shells, form when a foreign body such as a sand grain becomes lodged inside the shell. To stop it irritating, the animal slowly surrounds it with nacre.