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THEOPHRASTUS ON STONES
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However, his statements in section 48 of the treatise, where finished ceramic ware is described as stone, suggest that he would not have made any such distinction in classification. Judging from the reference Theophrastus makes to glass and vitreous earth in section 49, it is doubtful that he was aware of the artificial origin of glass; and even if he understood its mode of origin, it does not follow that he would have recognized that seals executed in paste were not made of a natural material, for since they were engraved, they were very different in appearance from large objects made out of glass by other methods.
30. anthra\ion. This is mentioned again in section 33. See the notes on that section.
30. omphax. The Greek word δμφαξ usually means an unripe grape or some other unripe fruit, but it was often used in a metaphorical sense.204 Perhaps Theophrastus is using it in this way here, as he appears to be the only author to give ομφαξ as the name of a stone. Galen205 lists a stone with a similar name called όμφατΐτις {omphatitis), but, like Theophrastus, he gives no description. The name suggests that the stone resembled an unripe grape, i.e., it was green in color and in its natural state botryoidal. Furthermore, it is probable that it was either transparent or translucent, since the other stones discussed in this part of the treatise were not opaque. Practically the only mineral suitable for engraving that fulfills these conditions is prehnite, a hydrous calcium aluminum silicate usually colored apple-green by impurities and occurring normally in botryoidal masses lining cavities in igneous rocks. Prehnite is capable of receiving a high polish and has been used in modern times for inlaid work and ornaments.206 However, ancient engraved stones of prehnite have apparently not been found, and though this may seem to bring the identification into question, it should be noted that surviving examples of ancient non-opaque green stones are scarce,
204 Liddell-Scott-Jones, Gree^-English Lexicon, s.v.
205 j}e simplicium medicamentorum temperamentis ac facultatibus, IX (Kiihn ed., XII, 207).
206 Dana, Manual of Mineralogy and Petrography, pp. 317-18.
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