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Pisolite

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PLASMA.                                  181
LXXXI.
PLASMA.
under this name many people understand two differ­ent stones, thinking that the ancients confounded them together and called them prasius.
But I think that the prasina, or prasius of antiquity, is not the stone which, with more propriety, we now call plasma ; moreover, it appears to me they ought to be accurately distinguished.
I shall speak here of the plasma, and afterwards of the prasina, showing how this is not a variety of the plasma, and the ancients did not confound them, as it is said, one with the other, but that they indicated the plasma by a different name from the prasius, and perhaps by that of molochites.
The plasma is a semi-transparent agate, coloured green by some metallic oxide, probably copper or nickel ; although often in the purest quality it ap­proaches the colour of a fine emerald, yet it never possesses its brightness, is never pure, but always marked with little black and yellow spots.
Like the calcedony, it scratches glass deeply, and its specific gravity is from 2-58 to 2-66.
In colour it is dark olive, resinous, and semi-trans­parent. The extreme fineness of its texture renders it suitable for engraving.
It is found in the East and in the Black Forest. As we do not know exactly what name the ancients
Pyroxenum Page of 243 Plasma
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