Cu2Si2O5OH2

Cu2Si2O5OH2 is the chemical formula for a mineral known as dioptase. Dioptase is a hydrous copper silicate with the chemical composition Cu6[Si6O18](OH)6. The formula Cu2Si2O5OH2 represents a simplified or empirical formula rather than the full stoichiometry of the mineral. Dioptase is a rare, secondary copper mineral that typically forms in the oxidized zones of copper deposits. It is known for its striking emerald-green color and vitreous luster.

Dioptase crystallizes in the trigonal crystal system, often forming prismatic or rhombohedral crystals. It is relatively soft, with a Mohs hardness of 5, and has a specific gravity of around 3.3. This mineral is insoluble in water and most acids, though it can be dissolved in hot hydrochloric acid. Dioptase is often associated with other copper minerals such as chrysocolla, malachite, and azurite. It is also found in association with quartz and calcite.

While dioptase is not a significant ore of copper due to its rarity, it is highly prized by mineral collectors for its aesthetic appeal. It is found in various locations worldwide, including the Congo (DRC), Namibia, Kazakhstan, Chile, and the United States. The chemical formula Cu2Si2O5OH2, though simplified, highlights the presence of copper (Cu), silicon (Si), oxygen (O), and hydroxyl (OH) groups as the fundamental components of its structure.