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Geology

Jurassic Greenstone, Pacheco Pass Calif.

In the Picture Gallery of Metamorphic Rocks

Basaltic rocks from oceanic crust become greenstone with subduction's high pressure. Extremely old Archean greenstones probably have a different origin.
Tortured Jurassic ocean crust
Photo (c) Andrew Alden, licensed to About.com (fair use policy)

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Gallery Index: Metamorphic Rock Gallery

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