mineralphase

Mineral phase is a concept in geology and materials science describing a thermodynamically distinct, homogeneous state of a mineral material with a defined chemical composition and crystal structure. A mineral phase exists under specific pressure-temperature-composition (P-T-X) conditions, and may be stable, metastable, or transient.

Within a rock or mineral assemblage, multiple phases may coexist, each representing a distinct region with its own properties. Phase relations are depicted in phase diagrams that show which phases are stable at given P-T-X conditions. Changes in conditions can induce phase transitions, converting one mineral phase into another, a central process in metamorphism and igneous differentiation.

Many minerals exhibit polymorphism, where the same chemical formula forms different crystal structures (for example, alpha-quartz and beta-quartz; calcite and aragonite). Others form solid-solution or non-stoichiometric phases where composition varies continuously within a single crystal framework, such as plagioclase feldspars with varying calcium-sodium content. High-pressure, high-temperature phases of common minerals also exist, such as coesite and stishovite (SiO2).

Identification and study of mineral phases rely on techniques such as X-ray diffraction, electron microscopy, and spectroscopy, which determine crystal structure and composition. The concept of mineral phase is essential for understanding rock textures, metamorphic grade, mineral stability, ore genesis, and weathering behavior, as phase stability governs mineral abundances and reactions within rocks.

See also: phase diagram; polymorphism; phase transition; solid solution.