or Plaster-stone, in natural history, a genus of fossils, naturally and essentially simple, not inflammable nor soluble in water, and composed of flat small particles, which form bright, glossy, and in some degree transparent masses, not flexible or elastic, not giving fire with steel, nor fermenting with, or being soluble in, acid menstrua, and very easily calcined in the fire.

Of these gypsums, some are harder, others softer, and are of several colours; as, white, grey, red, green, &c. sometimes distinct, and sometimes variously blended together.

The texture of all the gypsums being ultimately the same, it may be sufficient to observe, that their origin is plainly from particles of a determinate nature and substance, and of a certain and invariable figure, an oblong, flat, and irregularly angular one. These we sometimes see, as indeed is most natural to them, disposed without order or regularity, into loose, complex, friable masses; at others, they are getting out of their native order, and emulating the structure of other classes of bodies, of which they are indeed properly the basis, and appearing somewhat in the figure of the fibranite; and at other times, of the foliaceous composite flakes of the selenite: the species which have these structures, are truly varying from the gypsums into those bodies they emulate; for the fibranite are only a peculiar arrangement of these very particles, and the selenite only more broad flakes of the same, like those of the foliaceous tales.

The gypsums are much used in plaster, for stuccoing rooms, and casting busts and statues.