Dioptase is one of the most gorgeous and valuable minerals on Earth due to its high quality crystallization, amazing color, and rarity. Chemically, dioptase is a trigonal hydrated copper silicate- CuSiO3·H2O. It forms large rhombohedral crystals in oxidized copper ores that grow up to 3cm, though very uncommonly they can be larger. Dioptase is commonly associated with calcite and quartz as well as many other copper and lead secondary minerals such as malachite, chrysocolla, plancheite, shattuckite, wulfenite, descloizite, mottramite, and duftite, all of these forming from weathering hydrothermally formed copper sulfides. Dioptase requires natural buffering of acidic solutions leaching from weathering copper sulfides to form because the solubility of silica and silicate anions in aqueous solution is proportional to pH and steeply reduced at lower pHs. Buffering is often facilitated by the presence of calcite in limestone. The calcite dissolves when attacked by protons in acidic solutions forming water and carbon dioxide which is emitted as a gas. Typically, when this kind of acid buffering occurs, chrysocolla is formed but under rare circumstances where the concentrations of copper and dissolved silica are correct and gorgeous crystals of dioptase grow!