Why are Diamonds Expensive?
This is mostly due to rarity. When mining Diamonds approximately 23 tonnes of earth are excavated to yield 5 carats (1 gram) of weigh in diamond. Furthermore, only 20% of the diamonds found are suitable for jewellery; others are used for industrial purposes.

I heard there was a Conspiracy to Conceal the Number of Diamonds found in order to Raise the demand and Price of the Diamonds already available.
Like most conspiracy theories this is a mixture of misunderstanding and false information. Most diamonds contain serious flaws and are unsuitable for jewellery; about 80% are only suitable for industrial use. Decent quality diamonds are fairly rare; high quality diamonds more so.

There are also some serious human right issues with diamonds mined in certain parts of the world. Sales of some diamonds are purportedly used to finance dishonest political schemes and serve to exploit many individuals. Sales of these diamonds have been banned for ethical reasons, not to increase their value.

What makes one diamond more valuable than another?
Colour – being a pure white diamond makes the stone more valuable, but a pure coloured is rare, and also very valuable. Mixed or impure colours are less desirable.
Carat – this is basically the weight/size of the diamond. All things being equal, a larger diamond is with more, though colour and lack of flaws are also highly important.
Cut – It takes great skill to cut a diamond properly, and the result affects its value. The cut of a diamond determines its internal reflection of light, and hence its appearance. A good cut make all the difference to the value.

What is an ‘Ideal’ diamond?
This does not mean a perfect diamond – no such thing exists. An ‘ideal cut’ is one that allows for the best internal reflection of light, making the stone ‘sparkle’. There are several opinion and variations of the ideal cut; several different cuts achieve this optimal sparkle.

Diamonds are hard, but apparently they can break?
Diamonds are very hard, and can scratch anything. But they can be shattered if hit at the wrong point across the grain. This is rare, but catastrophic.

Are diamonds good Investments?
Diamonds are not good financial investments as prices are unpredictable. But as they are extremely long lasting they are good emotional investments.