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retrograde metamorphismIn the mountains last week I picked up a cool-looking garnet schist. But curses, the garnets had been resorbed! I was victim once again to retrograde metamorphism. Now I'll have to wait until I've acquired that coveted thin-section machine and petrographic microscope before I can study what happened. It's rather common for rocks coming down from high pressures and temperatures to revert to minerals that are stable at less extreme conditions. At least I got a new thing to put into the Geologic Features and Processes Gallery.

Ex-garnet schist — Geology Guide photo


October 9, 2006 at 2:51 am
(1) David Hilyard says:

And retrograde metamorphism is why diamonds need the high-speed elevator of a kimberlite diatreme to get them from mantle depths to the surface, without turning into common or garden graphite.

October 9, 2006 at 5:09 pm
(2) Geology Guide says:

Very true, and I will add that to the diamond page.

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