A gemstone (or gem, fine gem, jewel, precious stone, or semi-precious stone) is a piece of mineral crystal which, in cut and polished form, is used to make jewellery. Certain rocks, including lapis lazuli and opal and some organic materials that are not minerals (such as amber, jet, and pearl) are also used for jewellery and are therefore often considered to be gemstones as well.

Most gemstones are hard, but some soft minerals are used in jewellery because of their sheen or other physical properties that have aesthetic value. Rarity is another characteristic that lends value to a gemstone.


When considering a coloured gemstone in an engagement ring or other jewellery it is important to choose a stone which is not just pleasing to the eye but which will withstand regular wear and impacts.

A natural diamond has a hardness of 10 on the Mohs scale. Sapphires and rubies have a hardness of 9 which is one of the reasons they have proven popular over the years in jewellery design.

Emeralds possess a hardness rating of 8 with aquamarines, amethysts, opals and tanzanite between 6.5 and 7. Gemstones much below this Mohs rating are less suitable for use in jewellery which will be worn on a regular basis.