is a stone resembling the onyx in colour, but, in place of zones, is adorned with lines or spots of various colours, which run into so many figures, as to resemble trees, flowers, fruits, herbs, &c. Of the agat there are several species, distinguished from each other chiefly by their colour; as, the white-veined agat, the lead-coloured agat, the flesh-coloured agat, &c.

is also the name of an instrument used by gold-wire-drawers, so called from the agat in the middle of it, which forms its principal part.