Naturalis historia 37.56: Adamas (diamond) of India

37.56

nunc primum genera eius sex noscuntur: Indici non in auro nascentis et quadam crystalli cognatione, siquidem et colore tralucido non differt et laterum sexangulo levore, turbinati in mucronem e duabus contrariis partibus, quo magis miremur , ut si duo turbines latissimis partibus iungantur, magnitudine vero etiam abellani nuclei. similis est huic Arabius, minor tantum, similiter et nascens. ceteris pallor argenti et in auro non nisi excellentissimo natalis.

At the present day, for the first time, there are no less than six different varieties of it recognized. The Indian adamas is found, not in a stratum of gold, but in a substance of a kindred nature to crystal; which it closely resembles in its transparency and its highly polished hexangular and hexahedral form. In shape it is turbinated, running to a point at either extremity, and closely resembling, marvellous to think of, two cones united at the base. In size, too, it is as large even as a hazel-nut. Resembling that of India, is the adamas of Arabia, which is found in a similar bed, but not so large in size. Other varieties have a pallid hue like that of silver, and are only to be found in the midst of gold of the very finest quality. These stones are tested upon the anvil, and will resist the blow to such an extent, as to make the iron rebound and the very anvil split asunder. Indeed its hardness is beyond all expression, while at the same time it quite sets fire at defiance and is incapable of being heated; owing to which indomitable powers it is, that it has received the name which it derives from the Greek.