A large family of minerals. They are quartz, but are translucent to opaque, rather than forming transparent crystals like many quartzes. They are usually not given a faceted cut because they aren't transparent; mostly they are made into cabochons or beads when used in jewelry.
The family contains agate, bloodstone, blue chalcedony, carnelian, chrysoprase, jasper, onyx, petrified wood, prase, sard, and sardonyx.