Roman Imitation Diamonds

This can happen even today. Go to any commerically important diamond + colored stone mines in the world + diamond and colored stone trading centers, and guess what, you will always find someone with imitations waiting for you. I believe this trend will continue forever.
(via The Journal of Gemmology, Vol. 13, No.5, January 1973) Jack M Ogden writes:

The use of diamond in Roman times is well attested but was by no means common. It is thought to have been introduced from the East sometime about 4th century B.C, possibly as a result of Alexander the Great’s conquests in the East. It is found set in rings and other jewelry in the Late Roman Period and the writer knows of no instances of its use prior to the third Century A.D.

The Romans were unable to cut diamonds due to their great hardness and all attested Roman diamonds are mounted in the naturally occurring form—octahedral crystals. The impossibility of cutting, no doubt, encouraged the name ‘Adamas’ meaning ‘invincible’, the word from which our ‘diamond’ comes. It would seem, however, that although the Romans were unable to alter the shape of natural diamond they had no hesitation in copying the shape in other materials, a 2000-year old case of ‘if you can’t beat it, join it’.

A Roman ring found in Syria and now in the hands of the writer is set with a clear, colorless octahedral stone which, although whiter than the usual murky Roman stones, could, at first glance, be taken for a diamond. In fact the stone is quartz cut into an octahedral form. This ring is by no means unique and several other examples are known by the writer. The explanation must surely be that the Roman jewelers were consciously imitating diamonds.

Glass imitations of gemstones are common in classical times and, indeed, are known from the earliest periods in Egypt and Western Asia. Normally these imitations are purely color copies and were cut in the usual shapes of the period. The copying of a crystal shape, as with the octahedral quartz, is obviously due to the impossibility of cutting diamonds and, thus, the octahedral quartz copied the only known shape of diamond. Other copying of crystal forms is possibly to be found in Roman times, a bracelet, also in the hands of the writer, is composed of red glass beads of Romano-Egyptian origin of cornerless cube shape, a shape known from as early as 500 B.C (Glass beads from Crimea). It is tempting to equate these with small garnet crystals. A ring in the British Museum is set with a green chalcedony cut to form a hexagonal prism, surely an imitation of an emerald. This chalcedony, often called ‘plasma’ in books on Ancient Jewellery, has whitish blotches and gives a good imitation of poor quality emeralds.