Pegmatite, a light-colored granite, forms bright stripes on the otherwise dark walls of the Black Canyon of the Gunnison in Colorado. These stripes were found on the Painted Wall, an especially dramatic part of the national park and the highest cliff in all of Colorado. Pegmatite is the result of especially water-rich magma, which is the last to cool and harden. Because it remains fluid longer, it is able to squeeze into cracks in rocks, resulting in the light-colored lines here.
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