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Jaspis, Jasper, Quartz-gems

Jaspis, Jasper, Quartz-gems Page of 384 Jaspis, Jasper, Quartz-gems Text size:minus plus Restore normal size   Mail page  Print this page
144                 NATURAL HISTORY OF GEMS.
parte, nec praeter margines quidquam auro amplectente." The extremely globose form given to all antique Plasmas and Amethysts strikingly corroborates this observation; showing that they necessarily wero intended for setting without a back.
The conclusion to be derived from all the foregoing details is undoubtedly this, that the Jaspis of the ancient« was our Calcedony (silica combined with alumina)—in its primary sense signifying the variety coloured green by nickel, now called Plasma, but in after times embracing the blue, the purple, the yellow, the whitey-brown shades of the same substance ; in a word, every colour except the blood-red, which gave its name and honour to the Sard. This decision is furthermore confirmed by the authority of Ben Mansur, dividing his Jasheb (the original of the Greek Iaspis) into five kinds : the White clear, the White-yellow, the Green-black, the Black-transparent, the Dust-coloured : or in modern parlance, the White Carnelian, the Yellow and Olive Sard, the Brown Sard (ßardoine), and the light Brown.
The modern Jasper, as distinguished from the modern Agate only in its being more opaque and containing more iron in its composition, was certainly regarded by the an­cients as a variety of the Achates. Of this we shall now proceed to consider the kinds that were chiefly employed by the engravers of antiquity.
1. First in the class stands the Black Jasper, an ex­tremely fine, close-grained substance, perfectly opaque, and thus distinguishable from the Black Agate (to which the ancients were equally partial), which is translucent and reddish-brown by transmitted light. This stone takes a high polish, the good preservation of which declares the uncommon density of its particles. It has been employed by the Greeks as the material for some of their finest
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