Ad
related to: andalusite trimorphic
Search results
Results From The WOW.Com Content Network
Andalusite is trimorphic with kyanite and sillimanite, being the lower pressure mid temperature polymorph. At higher temperatures and pressures, andalusite may convert to sillimanite. Thus, as with its other polymorphs, andalusite is an aluminosilicate index mineral, providing clues to depth and pressures involved in producing the host rock. [5]
Andalusite. Sillimanite. Phase diagram of Al 2 SiO 5 (aluminosilicates). [1] Template documentation. Usage. Add {{Al2sio5 phase diagram}} to the page. Source. Based ...
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.
Phase transitions (phase changes) that help describe polymorphism include polymorphic transitions as well as melting and vaporization transitions. According to IUPAC, a polymorphic transition is "A reversible transition of a solid crystalline phase at a certain temperature and pressure (the inversion point) to another phase of the same chemical composition with a different crystal structure."
Chiastolite (/ k aɪ ˈ æ s t ə ˌ l aɪ t / ky-ASS-tə-lyte) [1] is a variety of the mineral andalusite with the chemical composition Al 2 SiO 5. It is noted for its distinctive cross-shaped black inclusions of graphite. The presence of these crosses caused the mineral to be used as a gem.
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.
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: Author: Smith609: Permission (Reusing this file)
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).