Water of crystallization degree of hydration can be critical to the resulting chemical properties. For example, anhydrous RhCl is not soluble in water and is relatively useless in organometallic chemistry whereas RhCl•3HO is versatile. Similarly, hydrated AlCl is a poor Lewis acid and thus inactive as a catalyst for Friedel-Crafts reactions. Samples of AlCl must therefore be protected from atmospheric moisture to preclude the formation of hydrates. Crystals of hydrated copper(II) sulfate consist of [Cu(HO)] centers linked to SO ions. Copper is surrounded by six oxygen atoms, provided by two different sulfate groups and four molecules of water. A fifth water resides elsewhere
Mineral alteration Mineral alteration Mineral alteration refers to the various natural processes that alter a mineral's chemical composition or crystallography. Mineral alteration is essentially governed by the laws of thermodynamics related to energy conservation, relevant to environmental conditions, often in presence of catalysts, the most common and influential being water (HO). The degree and scales of time in which different minerals alter vary depending on the initial product and its physical properties and susceptibility to alteration. Some minerals such as quartz and zircon are highly resistant to alteration under normal weathering conditions. Yet quartz may alter to stishovite with intense pressure, and