[quote=MDinanaAs an aside.... do rocks really "decompose?" I'm sure there's a correct word for the process of them breaking down. Anybody know it? [/quote]

Decomposed Granite (DG for short) is the commonly used term in Geology and Soils Engineering for granitic (and often other similar igneous rocks) that has lost the bond between the individual grains. The process of weathering is responsible for the loss of bond.

Respectfully,

Jerry