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The stability fields of the Al 2 SiO 5 minerals polymorphs. 1, 2 and 3 are the stability fields of Kyanite, Andalusite and Sillimanite respectively. TP is the triple point, where, theoretically the three aluminosilicates minerals exist in equilibrium.
Printable version; In other projects ... Kyanite. Andalusite. Sillimanite. Phase diagram of Al 2 SiO 5 (aluminosilicates). [1] Template documentation ...
Own work using data from Whitney, D.L. (2002), “Coexisting andalusite, kyanite, and sillimanite: Sequential formation of three Al2SiO5 polymorphs during progressive metamorphism near the triple point, Sivrihisar, Turkey”, in American Mineralogist, volume 87, issue 4, pages 405–416
An example is provided by the aluminium silicate minerals, kyanite, andalusite, and sillimanite. All three have the identical composition, Al 2 SiO 5. Kyanite is stable at surface conditions. However, at atmospheric pressure, kyanite transforms to andalusite at a temperature of about 190 °C (374 °F).
Andalusite, kyanite, and sillimanite are the principal aluminium silicate minerals. [2] [3] [4] The triple point of the three polymorphs is located at a temperature of 500 °C (932 °F) and a pressure of 0.4 GPa (58,000 psi). These three minerals are commonly used as index minerals in metamorphic rocks.
The side of the diagram between calcite and sillimanite has a point added for anorthite (calcium feldspar), corresponding to an equal mixture (by mole percentage) of the two components. This forms pure anorthite. Likewise, points are added for clinopyroxene and garnet and the diagram is divided into subtriangles, as depicted in the accompanying ...
Andalusite is a common metamorphic mineral which forms under low pressure and low to high temperatures. The minerals kyanite and sillimanite are polymorphs of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to ...
Triangular diagrams showing the aluminium (A), calcium (C) and iron (F) content of the main phases (dark dots) in metamorphic rocks in various facies. Thin grey lines are stable phase equilibria. Triangular diagrams showing the aluminium (A), iron (F) and magnesium (M) content of the main phases (dark dots and, when the composition can vary ...