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Prasius, Plasma

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PRASIUS.
PRASIUS : ΤΙράσιος : Plasma.
The ancient Prasius, so called from the resemblance of its colour to the peculiar green of the leek (πράσον) is now included in the numerous class of green stones styled indiscriminately Plasma by the antiquary. This word, formerly written Prasma, whence the French name, Prisme d'Emeraude (the origin of the absurd designation Boot of Emerald) is merely the Italian cor­ruption of Prasina, according to their common vulgarism of changing Ε into L and vice versa. Under the Lower Empire, when the slang of the circus had become the current language, Prasinus, the colour of the Green faction, came to denote that particular shade to the exclusion of the more general word Viridis. Hence we find the panegyrist (in Symmachus) using the word Prasini instead of Smargdi ; and Epiphanius (XII. Stones of the Breastplate, iii.) remarking that the Smaragdus is called also the Prasius.
The Plasma is merely translucent Calcedony coloured green by some metallic oxide, of copper when dark, of nickel when of a brighter shade. It is in fact a nearly transparent green Jasper, and though frequently approximating in colour to the finest Emerald, it is seldom quite pure, but marked with black spots, or yellow patches, betraying its proper species. There is, how­ever, a pale-green variety, of which ring-stones are found per­fectly free from all such blemishes, and remarkably transparent. Such are specimens of the true Prasius of the ancients, their tint exhibiting an exact resemblance to the colour of a leek. These greatly resemble the true Emerald in their oily, soft tint, though they have not its peculiar lustre ; and these were without doubt the Smaragdi, which the Greeks speak of as being engraved for signets. Pliny indicates exactly the species, by noticing that
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