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| This slab of banded gneiss shows a series of in-echelon fractures (filled with aplite, an intrusive rock composed of quartz and feldspar minerals). The cell phone is 4 inches long for scale. This slab is along the Ryan Mountain Trail. Rocks like this form at depths and pressures in the range of 8 miles to possibly as much as 40 miles deep in the crust. The fact that they are exposed on the surface of a mountain peak is a testament to the ongoing tectonic uplift and erosion forces changing the landscape. |
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