Chalcedony Wikipedia
Chalcedony (/ k æ l ˈ s ɛ d ə n i /) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is ''s standard chemical structure (based on the chemical structure of quartz) is SiO 2 (silicon dioxide).