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USGS CMG InfoBank: Minerals and Weathering

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Comment: 09:40 - 10:44 (01:04)
Source: Annenberg/CPB Resources - Earth Revealed - 15. Weathering and Soils
Keywords: "J. Lawford Anderson", granite, weathering, mineral, temperature, quartz, feldspar, "chemical weathering", plagioclase, clay, orthoclase, sediment, rock, "sedimentary rock"

Our transcription: Granite is composed of various minerals formed over a range of temperatures.
Each mineral type responds to weathering differently.
Here's an example of a granite that's fresh, it's unweathered, and as I try as I might, I can't break this rock apart.
We can see the dark gray quartz and the pink orthoclase feldspar, they're in the rock but they haven't weathered.
We'll now turn to another granite that is already begun chemical weathering.
It's starting to fall apart.
And we find that the different minerals are proceeding differently.
Plagioclase is weathering the fastest, and has already turned to clay.
Orthoclase feldspars is starting to weather as well, but the quartz is not weathered at all.
But the basic framework of the rock is beginning to fall apart and now this rock, well you know, I can begin to break this rock apart with my hands -- it is starting to decompose.
And this is how a rock changes to become sediment.
The grains are breaking apart are dislodged and now will fall into the sedimentary system.

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Page Last Modified: Thu Oct 31 04:26:51 PDT 2013  (chd)