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Catoctin Greenstone
You will be in a high canopied forest strewn with large boulders beside the trail. The rocks here are primarily “Catoctin greenstone.” Greenstone forms a long, continuous band in the Blue Ridge throughout much of Virginia and all the way up to southern Pennsylvania. Greenstone was formed from lava flowing 600 million years ago. Heat, pressure, and aqueous mineral solutions changed the original basalt to greenstone. When the rock first reached the surface as molten lava, gases separated in part of it and the gas bubbles were “frozen” as holes when the lava solidified. The holes later filled with minerals such as quartz, green epidote, and green malachite (containing copper). The holes weathered away in some places, leaving
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