A mineral with a formula that is stoichiometric with respect to the asymmetric unit of the cell, and therefore reflects a lack of solid solution.
See solid solution for an example, also see asymmetric unit

A redundant term for halloysite and its use should be discontinued.

An orthorhombic (space group Pbca) pyroxene, with an end-member composition of Mg₂Si₂O₆. Enstatite and ferrosilite, Fe₂Si₂O₆, form a continuous solid solution series (with <5 mole % of CaSiO₃). Enstatite commonly occurs in mafic and ultramafic igneous rocks and some high-grade metamorphic rocks (granulite facies). Polymorphs of enstatite include a low- temperature, monoclinic form (clinoenstatite) and a high-temperature, orthorhombic form (protoenstatite) that may also occur naturally in nanocrystallite form. Ca-rich exsolution lamellae in enstatite crystals are common.
See pyroxene group for additional details.

Enthalpy, H, is a thermodynamic state function equal to internal energy plus the product of pressure times volume or H = E + PV, i.e., the heat content of the system. For example, the change in enthalpy, ΔH, is the heat involved, either released (exothermic) or absorbed (endothermic), in a system for a constant pressure process (e.g., a reaction at a fixed pressure). Exothermic reactions have a negative enthalpy change, whereas endothermic reactions have a positive enthalpy change. See state function, entropy

A thermodynamic state function, which is classically defined as a change, ΔS, in a system involving reversible heat (q_rev) in a process and absolute temperature (T), such that ΔS_sys = q_rev/T. A reversible heat process implies an equilibrium process, and thus the change in entropy allows the determination of the favored direction of a process or reaction. If the total entropy change is positive from the initial state to the final state, the process spontaneously occurs. Where an increase in entropy, ΔS, is positive, this indicates a greater degree of motion or randomness of atoms, molecules, or ions in a system.
See enthalpy, Gibbs energy, state function

A (bio)molecule that serves as a catalyst for a chemical reaction.

A trioctahedral member of the true mica group. The end-member formula is NaLiAl₂(Al₂Si₂)O₁₀(OH)₂. Ephesite occurs as the 1M and 2M₁ polytypes. Ephesite has been identified in pegmatite as a hydrothermal alteration product with analcime and natrolite from the Ilimaussaq intrusion, Greenland, and in manganese ore from Postmasburg, South Africa.

A poorly defined material, possibly an altered chlorite.

A poorly defined material, possibly a muscovite and K-rich feldspar pseudomorph after cordierite.

A poorly defined material, possibly illite.