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Joshua Tree National Park -
Geology Tour Road:
Pinto GneissThe banded and folded Pinto gneiss, approximately 1.7 billion years old, is most likely the oldest type of rock in the park. Gneiss, a metamorphic rock, has undergone change in mineral composition, grain size and orientation due to increases in pressure, heat and chemical activity. Gneiss, prior to its change, was a sedimentary rock. With directed pressure, mineral grains segregate and band together; this alternate banding of light and dark minerals is what defines a gneiss.
Brightly colored splotches found on the gneiss are a primitive form of plant life called lichens. Lichens are a mutually beneficial composite of fungi and algae. The various colors indicate different species. Some species form a weak carbonic acid, the primary agent in the chemical breakdown of rock into soil.
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