Plasma

in mineralogy, a mineral of the nature of chalcedony, and by Gmelin arranged as one of its species. It is-of a green colour of various shades, mixed with brown, and the whole arranged in dots, clouds, and bands. occurs in ma , and in angular and rounded fragments inclosed in tale or sieatite. It has a feeble, greasy lustre, both internally. and exters nally. Its fracture is conchoidal pa ing to fine splintery. Its fragments are indeterminate and sharp-edged, It is translucent, and in thin pieces semi-transparent: its hardne is nearly equal to that of chalcedony: it is brittle, and easily frangible. Its proper geological situation has not as yet been ascertained; neither has it been submitted to chemical analysis. Jt is not uncommon in Italy and the Levant: it occurs near Bojanovik, in Moravia, imbedded in serpentine, and near Toeltsva, in Upper Hungary, in rounded pieces with hornstone. Sometimes it combines with heliotrope and chalcedony, forming agate.