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A glimpse at the basics of metamorphism facies and facies series…….this might help geology students @geologyrocks @geologypage @geologyrockzblog @metamorphism @geologyrocks @geologychronicles @geologystudyblr @geologystudent @geologystudy @geologystudies @geologystories
Thermodynamics
This metamorphic rock is extremely useful to find in the field as it catches a chemical reaction in progress. The pale blue mineral is kyanite and the pink mineral is andalusite, both polymorphs of aluminosilicate minerals. These minerals have the exact same chemical formula and will turn from one to the other depending on the pressure and temperature conditions. Kyanite generally is found at higher pressures than andalusite, while andalusite is found at lower pressures and generally higher temperatures (the third polymorph, sillimanite, forms at the highest temperatures).
If you look closely there are even single grains with pink at one end and blue at the other. This rock preserves conditions just after it crossed the boundary in pressure-temperature where kyanite reacts to form andalusite. The picture owner describes the kyanite as turning into andalusite, suggesting that the rocks were being metamorphosed to conditions where kyanite was stable and then pressure dropped; the reaction therefore literally tracks how the pressure and temperature of the rock changed during metamorphism.
This rock was found on the Isle of Mull, Scotland.
-JBB
Image credit: Anne Burgess http://www.geograph.org.uk/photo/2982832
