But what exactly is decomposed granite? I wasn't aware that a rock would decompose (in this lifetime at least).
Used all over the place out here in the West, mostly for landscaping pathways. It doesn't blow away like sand and is very compact-able.
This isn't naturally decomposed in anyway— it is a byproduct of other stonework.
Trade names include "Gold Fines" for a yellowy brownish stuff, and I've also seen grayish "stone-dust" which is a finer version which is used underneath paving bricks.
-Dave