162                   NATURAL HISTORY OF GEMS.
	distinguished by having for its chemical base the' earth Zirconia, peculiar to this family. This exactly resembles Amber in colour, refraction, electricity and levity, and the sole distinction is its excessive hardness. We find in it also the two kinds mentioned by the Greek naturalist: a dark orange, extremely agreeable in tint (the male); and a pale yellow of extraordinary lustre (the female). Another argument for their identity is the frequent em­ployment of the Jacinth by the Greeks, for intagli in early times, and by the Romans for carnei also. But for the latter purpose they preferred the darker kind, which, thai worked out, is extremely effective. The stylo of antiqne engravings in this gem is altogether peculiar, so as easily recognised even in the impression from such an intaglio. It is characterized by a certain fluidity (lavare bagnato) and roundness of all the lines, and a shallowness of engraving adopted apparently to avoid all risk of fracture in working so porous a stone. This porousness is manifest even to the naked eye, for a Jacinth held up against a strong light appears like a mass of petrified honey, or guava-jelly. This difficulty in the engraving is remarked by Theophrastus in the passage above quoted, such at least appears to be the meaning of the obscure expression, " ãéé/erai 8è «áú êáôåñãáóßá Tis áõôïß ðëßßùí." Çè alludes here to what he had just before said of the Srnarag-dus : " there is a particular mode of working this stone so as to give it lustre, for in its native state it is not brilliant." From the similarity of texture in the two there is reason to infer that he means by this peculiar mode that use of the Marcasite (instead of the usual Emery which Ben Mansur describes as the only possible method for polishing the Laal (Spinel), one variety of which he gives as yellow, another as green. For, as far as regards the peculiar lustre, texture, and electricity, as well as