Diamond has held pride of place as chief of precious stones ever since the discovery of the form of cutting known as the ‘brilliant’ revealed to full perfection its amazing qualities; and justly so, since it combines in itself extreme hardness, high refraction, large colour-dispersion, and brilliant lustre. A rough diamond, especially from river gravels, has often a peculiar greasy appearance, and is no more attractive to the eye than a piece of washing-soda. It is therefore easy to understand why the Persians in the thirteenth century placed the pearl, ruby, emerald, and even peridot before it, and writers in the Middle Ages frequently esteemed it below emerald and ruby. The Indian lapidaries, who were the first to realize that diamond could be ground with its own powder, discovered what a wonderful difference the removal of the skin makes in the appearance of a stone. They, however, made no attempt to shape a stone, but merely polished the natural facets, and only added numerous small facets when they wished to conceal flaws or other imperfections; indeed, the famous traveller, Tavernier, from whom most of our knowledge of early mining in India is obtained, invariably found that a stone covered with many facets was badly flawed. The full radiant beauty of a diamond comes to light only when it is cut in brilliant form. Of all precious stones diamond has the simplest composition; it is merely crystallized carbon, another form of which is the humble and useful graphite, commonly known as ‘black-lead.’ Surely nature has surpassed all her marvellous efforts in producing from the same element substances with such divergent characters as the hard, brilliant, and transparent diamond and the soft, dull, and opaque graphite. It is, however, impossible to draw any sharp dividing line between the two; soft diamond passes insensibly into hard graphite, and vice versa. Boart, or bort, as it is sometimes written, is composed of minute crystals of diamond arranged haphazardly; it possesses no cleavage, its hardness is greater than that of the crystals, and its colour is greyish to blackish. Carbon, carbonado, or black diamond, which is composed of still more minute crystals, is black and opaque, and is perceptibly harder than the crystals. It passes into graphite, which varies in hardness, and may have any density between 2·O and 3·O. Jewellers apply the term boart to crystals or fragments which are of no service as gems; such pieces are crushed to powder and used for cutting and polishing purposes.