A precious stone, of which there are several varieties; next to diamond, it is considered the most valuable of gems. The white and pale blue varieties, by exposure to heat, become snow white, and, when cut, exhibit so high a degree of lustre, that they are used in place of diamond. The most highly prized varieties are the crimson and carmine red; these are the oriental ruby of the jeweller; the next is sapphire; and last, the yellow, or oriental topaz. The asterias, or star stone, is a very beautiful variety, of which the colour is generally violet-red, and the form a rhomboid, with truncated apices, which exhibit an opalescent lustre. A sapphire of ten carats' weight is considered to be worth fifty guineas. An oriental ruby of thirty carats, without flaws, and of a perfect colour, is considered almost as valuable as a diamond of the same weight.