Chalcedony (玉髄, gyokuzui) is a mineral composed of microcrystalline quartz (the main component of crystal) that has aggregated and solidified very densely. It is transparent to translucent and comes in various colors such as white, gray, red, and green. Beautiful specimens are used as gemstones and ornamental stones. It is also called "chalcedony" depending on its color and pattern, and agate (瑪瑙, menou) is also a member of this group.