Onyx

Onyx is a banded chalcedony, a fine intergrowth of quartz and moganite, two silica minerals, usually seen in black and white bands, though some stones alternate light and dark shades of a single colour. Its bands lie parallel, where those of most agates swirl. The name comes from the Greek for a claw or fingernail. Much of the black onyx on sale has been dyed, a craft the Romans already knew, and many carvings sold as onyx are really banded calcite, a softer stone; the word has also been loosely given to banded marble, alabaster and other materials. Onyx has long been cut into cameos, intaglios, beads and cabochons, and in Egypt bowls were made of it by the Second Dynasty. Cunningham gives onyx projective energy, Mars and Saturn, fire and the god Mars, and counts protection, defensive magic and the damping of sexual desire among its powers; he says it was carved with the head of Mars or a figure of Hercules and carried for courage. Hall calls it a stone of strength and self-confidence that steadies you under stress, keeps a memory of what has happened to its wearer, helps release old grief and supports wise decisions.