SAND, in natural history, a genus of fossils, the characters of which are, that they are found in minute concretions; forming together a kind of powder, the genuine particles of which are all of a tendency to one determinate shape, and appear regular, though more or less compleat concretions; not to be dissolved or disintegrated by water, or formed into a coherent mass by means of it, but retaining their figure in it; transparent, vitrifiable by extreme heat, and not dissoluble in, nor effervescing with, acids. Sands are subject to be variously blended both with homogeneous and heterogeneous substances, as that of talc, &c. and hence, as well as from their various colours, are subdivided into a number of species.