Geology Reference
In-Depth Information
(a)
(b)
Figure 5.5.
The presence of intrusive veins traversing slopes (a) in the Rocky Mountains, near Boulder,
Colorado; (b) near Pine Creek, Northern Territory.
Later work, based on observations in many parts of the world, has confirmed that many granite
boulders develop in two stages. Meteoric waters, charged with gases, chemicals and biota, percolate
down and along joints. The rock immediately adjacent to the fractures is attacked by the moisture
(Lagasquie, 1978). Water reacts with micas and feldspars to produce clays. Solution, hydration and
hydrolysis are active. Water takes quartz (silica) into solution for though fragments persist in the
regolith they too eventually disappear (Trudinger and Swaine, 1979). Bacteria with a known prefer-
ence for quartz or kaolinite may facilitate entry of water. The processes are relatively slow though
perhaps not as slow as it has been supposed, with micas altered in decades, feldspars in centuries or
