in natural history, a genus of semi-pellucid gems, of an even and regular not tabulated texture, of a semi-opaque crystalline basis, and variegated with different colours, dispersed in form of mists and clouds, and, if nicely examined, found to be owing to an admixture of various kinds of earths, but imperfectly blended in the mass, and often visible in distinct molecular.

Of this genus there are a great many species, as the bluish-white chalcedony; the brownish-black chalcedony, or smoky jasper or capitus of the ancients; and the yellow and red chalcedony.

All the chalcedonies give fire readily with steel, and make no effervescence with aqua-fortis.