Sawed slab of amygdaloid breccia. Shenandoah National Park, Virginia.
Summary
Shenandoah National Park, Virginia. Sawed slab of amygdaloid breccia. Slab is from the outcrop on the south side of the road about 500 feet southeast of Big Meadows Lodge. The angular blocks are probably pieces of frothy lava crust that formed at the top of the flow. The crust was broken by continued movement of the still-molten lava beneath, and jumbled pieces were rafted along and were eventually frozen in place when the flow came to rest and solidified. During later metamorphism the amygdules and some of the interstices between the blocks were filled with white quartz and yellow-green epidote. Locally, part of the rock has been altered to epidosite, a fine- grained light-green aggregate of epidote and quartz. The arcuate lines in [...]
Summary
Shenandoah National Park, Virginia. Sawed slab of amygdaloid breccia. Slab is from the outcrop on the south side of the road about 500 feet southeast of Big Meadows Lodge. The angular blocks are probably pieces of frothy lava crust that formed at the top of the flow. The crust was broken by continued movement of the still-molten lava beneath, and jumbled pieces were rafted along and were eventually frozen in place when the flow came to rest and solidified. During later metamorphism the amygdules and some of the interstices between the blocks were filled with white quartz and yellow-green epidote. Locally, part of the rock has been altered to epidosite, a fine- grained light-green aggregate of epidote and quartz. The arcuate lines in the lower left are marks left by the saw when the specimen was cut. Specimen collected by Professor Ernst Cloos, Johns Hopkins University. Photo by J.P. Owens. Figure 12, U.S. Geological Survey Bulletin 1265.
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