in natural history, one of the semipellucid gems, with variously coloured zones, but none red; being composed of crystal, debased by a small admixture of earth; and made up either of a number of flat plates, or of a series of coats surrounding a central nucleus, and separated from each other by veins of a different colour, resembling zones or belts.

We have four species of this gem. 1. A bluish white one, with broad white zones. 2. A very pure onyx, with snow-white veins. 3. The jasperonyx, or horny onyx, with green zones. 4. The brown onyx, with bluish white zones.