When we speak of gemstones, we usually mean minerals that have been cut and polished. However, over the ages, humans have used a great variety of materials for decoration.

Minerals have been cut and polished, and organic materials like coral, pearls, amber and ivory have been fashioned. Small fossils are often set in jewellery. Widespread materials like horn, bone, shells, seeds, even wood abound, as well as made materials like glass and pottery.

Not all minerals are suitable for gemstones. As well as beauty, a mineral must possess hardness and stability, and occur in crystals or masses large enough for cutting. Such material is very rare. Many minerals are small, opaque or easily damaged. Of over 4000 known minerals, only about 100 minerals are ever worked and only about 20 are commonly used in jewellery.

A number of opaque minerals and rocks with attractive colours and patterns are polished to make beads, carvings, bowls and decorative items. Such minerals are broadly termed 'ornamentals'.

Collectors' gemstones

Some gemstones are too fragile for wear or use and yet they are faceted because of their beauty and rarity. These gemstones are known as collectors' stones and are prized by individual collectors and museums. They present a challenge to the cutter because of their softness, perfect cleavage or sensitivity to heat or light.

They are wonders of the cutter's art, often revealing unexpected worlds of beauty inside an unlikely mineral.