Properties of water equal to that of the hydrogen ion (), which gives a pH of 7 at 25 °C. Action of water on rock over long periods of time typically leads to weathering and water erosion, physical processes that convert solid rocks and minerals into soil and sediment, but under some conditions chemical reactions with water occur as well, resulting in metasomatism or mineral hydration, a type of chemical alteration of a rock which produces clay minerals. It also occurs when Portland cement hardens. Water ice can form clathrate compounds, known as clathrate hydrates, with a variety of small molecules that can
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