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USGS CMG InfoBank: Analyzing Rocks

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Comment: 13:29 - 14:51 (01:22)
Source: Annenberg/CPB Resources - Earth Revealed - 12. Minerals: The Materials of Earth
Keywords: "J. Lawford Anderson", petrologist, granite, "Whipple Mountains", "Colorado River", California, "rock age", "rock origin", crust, "laboratory analysis", mineral, "chemical composition", "rock slab", "thin section", microscope, mineral, intergrowth

Our transcription: Petrologist Lawford Anderson is analyzing a piece of granite from the Whipple Mountains, which lie along the Colorado River in Southeastern California.
The purpose of the investigation is to determine the age of the granite, as well as to figure out exactly where in the Earth's crust it originated.
That rock comes back to the laboratory. We're going to learn to read that part of Earth's history.
We've got to open that rock up like opening up a book and start to read what kind of secrets are pent up in its mineralogic or elemental composition.
One of the thing that happens is that we saw that rock, and from that slab of rock that's removed.
We have a piece of the rock here, and from the slab, we break it down to a smaller piece from which a very thin slice is made.
That is a layer of rock that is sliced so thin that we can pass light through it in a microscope to look down and see how the different minerals are arranged.
Be they sedimentary, igneous, or metamorphic minerals, the nature of the way they're intergrown, their composition tells us about the conditions of that rock's history, that part of Earth's history.

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