|
|
Individual grains of feldspar lie surrounded by soil. The minerals surrounding these large crystals have weathered to form clays, leaving more resistant feldspars behind.
|
Nibbling away the mountain
Once at the surface, granite falls victim to the slow, gnawing forces ofweathering and erosion. Water falling on the rock as rain or snow and groundwater percolating just beneath the surface begins to disintegrate the rock grain by grain.
Water and dust particles gradually work their way between individual mineral grains. Mica and feldspar grains in the granitic rock chemically react with the water and decompose to form clay minerals. Clay minerals and dust tend to swell-up when they get wet, then shrink when they dry out. These tiny particles act as wedges between more chemically resistant minerals, prying them loose from the solid rock, like the potassium feldspar grains in the image on the right. Over time, the granite ‘rots’ and streams begin to carry away the loose, rotten granitic soil.
|
View geologic map of area (large files!)
