The James River Park System - Richmond, VA

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South Geology Tour

Stop 2: Solid as a Rock

DIRECTIONS: Walk up the stairway and stop midway.

The rock on your right has been altered naturally by WEATHERING.

Weathering on rock

PHYSICAL WEATHERING -- Water and wind grind particles against the bedrock, sanding away the rock edges. The freezing and thawing of water in cracks also can disintegrate rock.

CHEMICAL WEATHERING -- Rainwater produces a weak acid that, over time, dissolves the biotite and feldspar in granite, causing the rock to decompose. As you climb the steps look for a granular, orange-yellow-brown material. You have found SAPROLITE. This coarse, sand-like material can be thought of as "rotten rock".

BIOLOGICAL WEATHERING -- The surface of granite can be etched by mild acids produced by LICHENS. These primitive plant-like organisms colonize bare rock surfaces and look like the remnants of weathered paint. MOSSES grow where moisture collects along cracks and in shaded depressions. Plant roots grow into small fractures seeking moisture. As the root grows, it wedges the rock apart.


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