Diorite

I have just read about the diorite in the section on rocks of Minerals, Rocks & Fossils by A. C. Bishop, A. R. Woolley, and W. R. Hamilton. I gather that xenoliths are common in this rock, whose constituent mineral feldspar or hornblende may form phenocrysts and make it porphyritic.

Everybody ought to know that geological rocks come in three varieties: igneous, metamorphic, sedimentary – and anyone who does not know this should be treated with the ridicule due to one contestant I once saw on “Eggheads” who thought Hawaii was in the Indian Ocean. Diorite, in particular, is igneous.