What makes diamonds valuable, and why do we revere them so much?

Why are we asking this now?

They are the ultimate in glitz and have been described as fragments of stars, or like tears of the gods. For thousands of years, mankind has been besotted by the beauty of the diamond. It is no surprise then that the discovery of what could turn out to be one of the largest examples of the gem has re-ignited our love affair with the stone. A 478-carat diamond, described by its finders as a "near-flawless" example, has been unearthed at a mine in Lesotho. It is now being pored over by experts in Antwerp, but it is already being touted as one of the biggest polished gems in history.

How big is this diamond, and how does it compare with others?

The stone was discovered earlier this month at the Letseng mine in Lesotho, by the mining firm Gem Diamonds. The company has said its value is hard to gauge before it has been cut and fitted to a piece of jewellery. But a similar-sized stone of lesser quality went for £6m recently. If it is cut and fitted in the right way, the new discovery could make millions more. Clifford Elphick, chief executive of Gem Diamonds, said: "Preliminary examination of this remarkable diamond indicates that it will yield a record-breaking polished stone of the very best colour and clarity."

Is Lesotho a key source of diamonds?

South Africa may be better known as a source of diamonds, but Lesotho, a country with a population of 2million and completely surrounded by South Africa, is a key exporter of the gem. (Its other main export is wool). The Letseng mine has developed something of a reputation for housing mammoth diamonds. The latest find is only the fourth largest diamond to be found there. The biggest, Lesotho Promise, weighed in at 603 carats. Originally, India was the principle source of diamonds, but that switched to Brazil and then to several African nations, including South Africa and Lesotho.

What exactly is a diamond?

For all its beauty, a diamond is actually an extremely simple material. It is made of pure carbon and is the hardest naturally occurring mineral. In fact, the only thing separating the precious stone from coal is its molecular structure (it's all in the isometric-hexoctahedral crystal lattice). Though the classic colour for a diamond is a dazzling white, they also naturally occur in shades of pink, cognac, blue, yellow and green.

Have diamonds always been so popular?

Yes, though diamonds have meant different things to different societies. Until the 15th century, they were seen by leaders as symbols of supreme strength. The name itself comes from the Greek word "adamas", meaning indestructible. The Greeks were a romantic sort, and for them the dancing sparkle of the diamond was the sign of the extinguishable flame of love.

Many have seen diamonds as having a magical quality – fuelled by the fact that many glow in the dark. As a result, they have been used as a cure for madness, to ward off evil spirits and devils, and even as a cure for nightmares. The Greek philosopher Plato was said to share the belief that diamonds were living spirits. Diamond "powder" has also been used as a potent poison – apparently one favoured by Catherine de Medici in the 16th century.

So why do we use them for engagement rings?

We have a particularly romantically-minded Austrian aristocrat to thank for that innovation. Archduke Maximilian decided to give his fiancée, Mary of Burgundy, a diamond ring when he proposed to her in 1477. It caught on, though the custom of wearing the ring on the third finger of the left hand (thought to contain a vein that led straight to the heart) has been around since the ancient Egyptians.