Why are minerals like diamonds and ruby so expensive whereas other minerals like coal and sulphur are not? No spammers.spammers will be reported​

A ruby is a pink to blood-red coloured gemstone, a variety of the mineral corundum (aluminium oxide). Other varieties of gem-quality corundum are called sapphires. Ruby is one of the traditional cardinal gems, together with amethyst, sapphire, emerald, and diamond. The word ruby comes from ruber, Latin for red.