Augite Andesite: P207

Title: Augite Andesite: P207
Description: The hand sample is an Aphanitic (fine-grained), dark colored rock with small visible grains of colorless plagioclase and black augite.

In he thin section one can see phenocrysts of plagioclase feldspar, augite, and magnetite in a microlite groundmass. The feldspars show some fantastic examples of zoning and twinning. The augite is pleochroic, changing from a yellow to a light-green. Hornblende can be found in thin section with a brown color. The large crystals with inclusions are apatite crystals.

This rock initially cooled slowly within a magma chamber, partitioning plagioclase feldspars, augites, and olivines and other mafic minerals, but the more mafic minerals may have sunk to the bottom of the chamber, but as it was cooling the magma heated up again, shown by the oscillatory zoning. Perhaps another, hotter magma was injected into it. After cooling slightly and fractionating, the magma erupted and cooled rapidly.
Creator: 4737
Type: Igneous Rock
Mediator: Tamara Carley

Media: https://exhibits.lafayette.edu/geology/files/original/356e80471f88d486714cf33ea83a0c28.JPG; https://exhibits.lafayette.edu/geology/files/original/f33a24171cbe3c260e2af7c25c391ed0.JPG; https://exhibits.lafayette.edu/geology/files/original/be9b059b7839153c78984f2670e4667b.JPG; https://exhibits.lafayette.edu/geology/files/original/fd02065a90eddca3c4c4078cd0e3dd8a.JPG; https://exhibits.lafayette.edu/geology/files/original/64816644107a16ca7c9f870f5233f353.jpeg; https://exhibits.lafayette.edu/geology/files/original/0be84fbeb31813621f7e7a4bbf0994a9.jpeg; https://exhibits.lafayette.edu/geology/files/original/69f90d96fe9810a1f5d9a58c4fe0d73f.jpeg; https://exhibits.lafayette.edu/geology/files/original/5c20b21f2e90b07c6cff7f9441fa9851.jpeg; https://exhibits.lafayette.edu/geology/files/original/14c9824174b929bf4608695f8ec4d110.jpeg; https://exhibits.lafayette.edu/geology/files/original/46cc87044d879bf0834f489ae2b3ede0.jpeg

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