Partly because I missed a week for various reasons, this week I offer something a bit different: fundamental to the practice of geology and mineralogy, but far different from pictures of volcanoes, geological formations, or remote-sensing from space. These are thin-sections; slices out of rocks viewed with a microscope (frequently with a polarizer to bring out remarkable and beautiful colors and patterns). First up: I don't know what this is, but there's a lot in it! Thin section from the Nakhla (Martian) meteorite, primarily pyroxene and feldspar: Monzonite porphyry: there's a bit more information on this one: "This rock is...