Chalcedony
Gemstone
Chalcedony 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 monoclinic.... Wikipedia
Hardness (Mohs hardness scale): 6.5 – 7
Chemical formula: SiO₂
Category: Silicate minerals, quartz group
Cleavage: Absent
Crystal system: Trigonal or monoclinic
Diaphaneity: Translucent