- Chalcedony
-
A subset of quartz. Chalcedony refers to cryptocrystalline quartz, that is, quartz whose crystals are too small to be seen, and includes agate, bloodstone, carnelian, chrysoprase, jasper, and onyx. This can be contrasted with macrocrystalline quartz such as amethyst, citrine, clear quartz, rose quartz, smoky quartz, and tiger’s eye. Here’s a thorough explanation.
