Onyx is a cryptocrystalline form of quartz. The colors of its bands range from white to almost every color (save some shades, such as Purple or Blue.) Commonly, specimens of onyx available contain bands of colors of white, tan, and brown. Sardonyx is a variant in which the colored bands are sard (shades of red) rather than black. However, pure black Onyx is still common, but not as common as Onyx with banded colors.
