You can't see it very well in this photo, but this random chunk of granite just about to be shaped already has a natural ninety degree plane appearing and has indications on its surfaces that it would be easy to break at right angles both to the bedding plane and the face plane. This seems to be the tendancy for much of this beautiful salt and pepper granite found along the Kern River Canyon and all around Lake Isabella in California. It is an amazing workable rock to use especially for squaring up corner stones. It is much different from the rubbery sandstone, the hard basalt and the flaky mica schist available out west, all which is difficult to split or pitch to even get a good face.
As you can see in the above shots, the rock was easily chiseled along the rest of the natural 'ninety' that had already 'showed up' in the stone.