CHALCEDONY, 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 mals, and often visible in distinct molecules.
Of this genus there are a great many species, as the bluish-white chaledony; the brownish-black chaledony, or smoky jasper or capnitis of the ancients; and the yellow and red chaledony.
All the chaledonies give fire readily with steel, and make no effervescence with aqua-fortis.