Click the photo to see the larger version. This eclogite specimen from Jenner, California, was part of a subducting plate during Jurassic times, about 170 million years ago, when it formed. Much more recently, during the last few million years, it was raised and mixed into younger subducted rocks of the Franciscan complex. The body of eclogite is no more than 100 meters across today. It consists of high-magnesium pyrope garnet, green omphacite (a high-sodium/aluminum pyroxene), and deep-blue glaucophane (a sodium-rich amphibole).
For more photos see the Eclogite Gallery.
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