metastable Applied to a phase which is apparently stable but is capable of reaction if disturbed, a state usually due to the slowness of a system to attain equilibrium. The term is applied, for example, to supersaturated solutions. A phase is said to be metastable if it exists in the same temperature range in which another phase with lower vapour pressure is stable. Many minerals that occur at room temperature and pressure are metastable (e.g. diamond) and most metamorphic rocks formed under high temperatures and pressures are metastable at the surface under normal temperatures and pressures. A metastable system (mineral assemblage) is in a temporary state of equilibrium and requires only a minimal disturbance to initiate a change to a state of true equilibrium. A gabbro mineral assemblage which crystallized at high temperatures and moderate pressures, and is thus in equilibrium under these conditions, would be in a metastable state when exposed by erosion to the low-temperature, low-pressure environment at the Earth's surface. Rainwater falling on the exposed mineral assemblage would act as the disturbance or catalyst initiating the reaction of the gabbro mineral assemblage to a low-temperature, low-pressure, chlorite—clay mineral assemblage, thus reestablishing the equilibrium.
More From encyclopedia.com
Diagenesis , diagenesis All the changes that take place in a sediment at low temperature and pressure after deposition. With increasing temperature and pressure,… Boiling Point , The boiling point of a liquid substance is the temperature at which the vapor pressure of the liquid equals the external pressure on the liquid. Vapo… Shock Metamorphism , Except for certain laboratory experiments and outdoor detonations of high explosives (including nuclear weapons), evidence of shock metamorphic condi… Vapor Pressure , Vapor pressure is the pressure that occurs because of the formation of vapor, or gas, from a liquid or solid. Within chemistry, this pressure general… Pressure Melting , pressure melting The melting of ice in response to stress. It comes about because the freezing temperature of water falls as pressure increases, at a… Thermometer , A thermometer is a device that registers the temperature of a substance relative to some agreed upon standard. Thermometers use changes in the physic…
About this article
All Sources -
Updated Aug 08 2016 About encyclopedia.com content Print Topic
You Might Also Like