Sapphire belongs to the Corundum family, set apart from other gemstones by their hardness and second only to Diamonds.

Blue is Sapphire's main colour, but it is a popular misconception that the deeper the blue the more valuable the Sapphire. It is in fact the middle blues, such as cornflower blue, that are the most sought after, fetching the highest prices. Sapphires are also found in pronounced shades of green, pink, purple, orange and yellow.

The best 'cornflower blue' Sapphires are Sri Lankan but superb specimens are also found in Kashmir and the USA. India, Burma, Thailand, Vietnam, Australia, Brazil, Russia and Africa all produce Sapphires with many of the fancy coloured Sapphires from Madagascar.

Sapphire is the birthstone for September.

Ruby is the red variety of the Corundum mineral, one of the hardest minerals on Earth, and its colour varies from a pale rose-red to deep carmine. Inclusions do not affect the quality of a Ruby, unless they decrease the transparency of the stone or are located right in the centre of its table.

Today the main sources of Ruby are Burma, Thailand and Sri Lanka. Ruby is found in very few places because the essential chromic oxide is a comparatively scarce substance making the best Rubies rare.

Ruby is the birthstone for July.

Emeralds vary in colour from deep to pale, watery green with the stone's colour and clarity both affecting its value. Emeralds are very often flawed and can contain numerous inclusions making a flawless stone a rarity.

Emeralds were mined in the Cleopatra Emerald mines near the Red Sea in Egypt, as early as 2000 BC. However, today the main sources of fine Emeralds are Brazil and the Colombian Andes but they have also been found in Russia, Australia, Africa, Pakistan and India.

Emerald is the birthstone for May.

Aquamarine is one of the most popular Gem Stones, usually almost free of inclusions with a good hardness and a breathtaking brilliance. The shades of an Aquamarine range from almost colourless pale blue through to bright sea blue - the more intense its colour the higher its value.

Brazil is the main source of Aquamarines although they are also found in other countries such as Nigeria, Madagascar, Mozambique, Afghanistan and Pakistan.

Aquamarine is the birthstone for March.

Australia is the traditional country of origin for this most highly prized of the silica Gem stones. Almost ninety five per cent of all fine Opals come from the dry and remote outback deserts.

Opals used in Jewellery include black, dark blue, dark green or grey with vivid flashes of colour springing from the dark stone; the orange-red of a Fire Opal which may or may not show a play of colour; Water Opal showing brilliant flashes of colour in a clear, colourless (water-white) stone. The iridescent colours of precious Opals are caused by the minute spheres of amorphous silica that make up the Opal interfering with the reflection of light, similar to oily water.

Opal is the birthstone for October.

Amethyst ranges in colour from pale lilac to deep purple. The pale colours are sometimes called 'Rose de France' and can be seen set in Victorian Jewellery. The deep colours are the most valuable, particularly a rich purple with rose flashes.

Amethyst is mined in Brazil, Uruguay, Bolivia and Argentina, as well as some African countries.

Amethyst is the birthstone for February.

Pearls are of organic origin with a crystalline structure. Cultured Pearls divide into two main groups, Freshwater Cultured Pearls and Seawater Cultured Pearls. Freshwater Cultured Pearls are genererally from Mussels in freshwater, in which many Pearls are produced while Seawater Cultured Pearls come from oysters which produce only one Pearl. Oyster pearls have a more even shape and a superior lustre. An irritant, often a mother of pearl bead for Cultured Pearls, stimulates the oyster to encase it in nacre, these layers forming the Pearl.

Lustre, colour, shape and clarity all determine the quality and value of a Pearl, lustre being the most important. For a Cultured Pearl to have good lustre it must have an adequate covering of nacre over the nucleus, and pearls that have not been left in the oysters long enough lack lustre. A Pearl's clarity is determined by the absence or presence of flaws including surface marks and internal spots. Cultured Pearls have different ground colours - white, silver, pink, yellow, green, gold and bronze. Fancy colours also exist, of which blue and black are the most common.

The effect of size on price is similar to that of all gems - the bigger the pearl the higher the price, and the rise in price from size to size is quite dramatic. A 16-inch string of 9mm pearls would probably cost nine or ten times as much as a string of 3mm pearls of the same length and quality.

Large Cultured Pearls (9mm and above) are also known as South Sea Pearls, where the larger pearls develop in the warmer waters. Pearls are sourced from Japan, China, the Persian Gulf, Sri Lanka and North-West coast of Australia.

Pearl is the birthstone for June.