DIAMONDS, it's said, are a girl's best friend, and no doubt rubies, sapphires and the like come a not-too-distant second. Precious gems have been coveted by kings and commoners alike through the ages as a sign of wealth and position. And there is a special gem to represent each month of the year.

The 12 birthstones are each said to bring a special gift to the wearer.

From folklore tales, Biblical texts, and the annals of history, these gems have had a special place in both the hearts and minds of humanity.

One of the first associations of gems with months of the year is in the Bible in Exodus, when a breastplate was made for the High Priest of the Hebrews. It is believed that birthstones originated from this 12-jewelled breastplate.

They were later linked with the signs of the Zodiac according to colour, and cultures through the centuries often attributed luck or special powers to the stones. Nowadays we associate gems with each month.

January's birthstone is garnet, which is generally thought to be a deep red, but in fact can be a variety of colours. It is a semi-precious stone and is thought to bring protection for travellers.

Once considered more valuable than diamonds, amethyst is linked to February and is said to strengthen the bond of love in relationships. It has a unique and striking purple hue, but like the garnet, is a semi-precious stone, as it is relatively common.

Aquamarine, the stone for March, is a very sensual blue colour symbolising safety and security and may even awaken love in a tired relationship.

While the beauty of any gem - measured using the four Cs: cut, clarity, carat and colour - governs value, rarity is also important in deciding the cost. The rarer the gem - such as diamonds, sapphires, rubies, or emeralds - the more precious it is.

Semi-precious stones, including garnet, peridot and amethyst, are no less appealing, but as they are generally more common, they are less expensive.

And it is April's gem, the diamond, which is the most prized stone. Zsa-Zsa Gabor once said she never hated a man enough to give his diamonds back. Diamond is the hardest substance on earth, and also regarded as the prettiest. A gift of a diamond shows everlasting love. How a diamond is cut and faceted reflects its value and popular appeal.

Val Higgins of quality jewellers Eric G Milton, in Liverpool, holds tradition dear to her heart, and for her, diamonds really are a girl's best friend. She says: ''Obviously my own birthstone is my favourite, but that's not just because it's a diamond. I prefer diamonds to any other coloured stone. They are the rarest, and I would always pick a diamond!''

Emerald is the gem for May, symbolising love and fidelity. It's deep, luscious green is very popular and large stones are very rare but emeralds require good care as they are easily damaged and relatively fragile.

June is the month for pearls or the moonstone. Natural pearls, however, are extremely rare and while 90 per cent of the world market is in cultured pearls, those who love them do so with unquenchable passion.

They are often described as nature's perfect gift, reflecting taste and refinement and many people regard them as a sign of purity. Their popularity peaked with the glamour of the 1960s, but now their appeal has waned slightly.

July's gem speaks of passion and love. The deep red ruby is a much coveted gem and larger ones are very rare and some of the most valuable in the world. Rubies are a sign of everlasting love, bringing good luck when worn on the left hand - making the perfect engagement ring.

Peridot is a striking colour for the month of August. Its dazzling pale green hue is said to reflect the force of nature and stands for both strength and new growth.

September's stone is the sapphire. The most popular sapphires are a rich blue, and due to their demand and rarity, are by far the most expensive. Many other colours may be found, but are even rarer.

The lucky opal is October's shimmering stone, even though it has long held fears of bringing bad luck to the wearer. The many colours of this semi-precious gem symbolise faithfulness and confidence and while demand is relatively low, some good quality gems are very expensive.

November's gem topaz is remarkably distinct and varies from shades of dark sherry through to a vibrant light orange and even a seductive blue. Topaz's striking tones reflect both love and fidelity.

Turquoise for December was once thought to be a sacred stone, but nowadays is more associated with luck. It is an opaque stone and not precious so relatively inexpensive.

In years gone by, jewels were often bought as an investment, as precious stones hold their value much better than hard cash ever could. The rarer the stone the better for the investor, as demand has a huge influence on price.

Nowadays however, few people consider gems as long term investments. It is the enduring beauty and uniqueness of gems that appeals to people. Each gem has a different character and attraction, which appeals to people in a different way.

The allure of birthstones today is as strong as ever. Whether they are precious or semi-precious stones, they make the perfect gift to mark events such as birthdays, wedding anniversaries and graduations.

Even in the 21st century of bling, the demand for a unique gem to mark a special day is still there.