Recrystallisation

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General impact of recrystallisation on the internal structure of the mineral:

  • Recrystallisation can destroys the internal structure of a mineral (e.g., growth zoning, exsolution) and other textures (graphic texture);

  • Phase separation: the minor phase (microinculsion) tend to coarsen and to be removed from the major phase – the minor phase can form grains along the margin of the major phase (e.g., gold and pyrite, ilmenite oxy-exsolutions and magnetite).

Annealing

Origin: rock maintained at a high temperature for a prolonged period (e.g., temperature anomaly related to a cooling magma intrusion or to a metamorphic event). Grain sizes tend to homogenize as small grains are consumed by other grains.

  • Texture: equigranular, with triple junctions (angle of 120 degrees if the mineral phases are of the same nature) that correspond to a minimization of the interstitial tension.

  • Granoblastic texture – homogenization of grain size (equigranular rock). This is a way to tend toward textural equilibrium.

    • Type of granoblastic texture: polygonal (with well developed triple junctions), interlobate, amoeboid, decussate, nodular (e.g., cordierite).

Decomposition

A mineral decomposes because it is not longer stable in the current physical-chemical conditions. These textures can also correspond to a reaction between two minerals that are no longer in equilibrium (e.g., metamorphic context).

  • Perthite (see the exsolution page)

  • Buldging recrystallisation – dynamic recrystallisation (see the deformation page)

  • Myrmekitic texture – vermicular intergrowth of quartz and plagioclase (has been attributed to hydrothermal replacement, or exsolution, or deformation, etc.).

  • Symplectite – fine-grained vermicular intergrowth (breakdown of minerals, or reaction between minerals under changing P-T conditions).

  • Mesh texture – olivine partially turned into serpentine (forms a serpentine mesh structure, with olivine core and serpentine background, as well as serpentine veins and magnetite veins).

  • Corona texture – new mineral developing at the contact between two older phases that are no longer stable in new P-T conditions (e.g., metamorphic reaction between magnetite and feldspar).

Recrystallisation in metamorphic context (no deformation)

  • Decussate (or diablastic) texture: randomly oriented mineral.

  • Phase change in the solid state: see the well studied lollingite and arsenopyrite + pyrrhotite example, and the consequence for the distribution of gold grains (see work of Tomkins).