tallio vapours, which, in the formation of the diamond, are introduced amongst the molecules.
Coloured
diamonds almost always preserve their transparency and limpidity. Some
of these, of a fine yellow, have often more light than the colourless
stones, hut some of these become dark, and even opaque, from the
presence of too much colouring material.
The
largest diamonds, in a rough state, were called " parangons," and,
according to their degree of purity and brightness, were said to be, as
at present, " of the first and second icaier." Small diamonds, partly rough, are called ' grani di sale." The
so-called " old rock " diamonds are all distinguished by extraordinary
light and purity, and are found in both the old and new world. Pliny
states that the hardness of the diamond cannot be equalled ; and that
it triumphs over fire, so that it cannot be warmed. In more recent
times, Cronstedt supposed that the diamond, considering its excessive
hardness, ought to be regarded as a formation of particular elements,
rather than of quartz and corundum.
De
Born, Scopoli, Pott, Cartheuser, and Wollendorf believed it to be
nothing but the purest earth. Bergman was the first who ranked it
amongst combustibles. Linnaeus said, the diamond was different from all
other gems. Buffon looked on it as a distillation of igneous material
produced from water. Guyton Morveau conjectured the diamond to be a
pure water deprived of that principle which, at a certain degree of
heat, renders it liquid. Baumé affirms that the diamond is
