ES2 Metamorphic Rocks - Metamorphic Microstructures #12
Nucleation effects: hornfelsic texture.
In contrast to the porphyroblastic texture of the previous slide, the contact-metamorphic hornfels, seen here at the same scale, shows abundant small grains of biotite. Rapid heating has caused the biotite-forming reaction to be greatly overstepped, allowing easy nucleation at very numerous sites.

Field of view is 2.5 mm across.

Cordierite-biotite hornfels, Comrie, Scotland, Sample 388.

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DJW - August 1997