Environmental Engineering Reference
In-Depth Information
PLATE 5.1 (
Color Plate 5.1
follows page 396.)
Pegmatite included into gneiss (Baltimore, Maryland).
PLATE 5.2 (
Color Plate 5.2
follows
page 396.)
Porphyritic biotite GRANITE with
phenocrysts of feldspar (St. Cloud,
Minnesota).
Rock Decay or Weathering
Processes
(see also
Section 6.7)
In mechanical weathering, the rock mass is broken into fragments as the joints react to
freeze-thaw cycles in cold climates, expansion-contraction, and the expansive power of
tree roots.
In chemical weathering, the rock mass is acted upon chemically by substances dissolved
in water, such as oxygen, carbon dioxide, and weak acids, causing the conversion of sili-
cates, oxides, and sulfides into new compounds such as carbonates, hydroxides, and sul-
fates, some of which are soluble.
