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phasePhase stability (equilibrium) diagramsphase stability boundary linesliquidussolidus

ssss1 A list of some common terms used in discussing phase diagrams.

Terms Definitions Liquidus Phase boundary (line) that separates the all‐liquid (melt) stability field from stability fields that contain at least some solids (crystals) Solidus Phase boundary (line) that separates the all‐solid (crystal) stability field from stability fields that contain at least some liquid (melt) Eutectic Condition under which liquid (melt) is in equilibrium with two different solids Peritectic Condition under which a reaction occurs between a pre‐existing solid phase and a liquid (melt) to produce a new solid phase Phase A mechanically separable part of the system; may be a liquid, gas or solid with a discrete set of mechanical properties and composition Invariant melting Occurs when melts of the same composition are produced by melting rocks of different initial composition Incongruent melting Occurs when a solid mineral phase melts to produce a melt and a different mineral with a different composition from the initial mineral Discontinuous reaction Mineral crystals and melt react to produce a completely different mineral; negligible solid solution exists between the minerals Continuous reaction Mineral crystals and melt react to continuously and incrementally change the composition of both; requires a mineral solid solution series Solvus Phase boundary (line) that separates conditions in which complete solid solution occurs within a mineral series from conditions under which solid solution is limited