in natural history, a genus of fossils of the harder gypsum, composed of very small particles, and of a less glittering hue.

There is only one species of this genus, being one of the least valuable and most impure of the clays of gypsums. It is of an extremely rude, irregular, coarse, and unequal structure; a little soft to the touch, of a very dull appearance, and of different degrees of a greyish white. It is burnt in plaster for the coarser works; it calcines very slowly and unequally, and makes but a very coarse and ordinary plaster.