Geology 101: What Is (and Isn't) a Mineral?

Geology is about rocks, and rocks are about minerals, so one of the first things a would-be geologist needs to learn is the definition of a mineral. Basically, minerals are solid, crystalline chemical compounds of inorganic origin. This article fleshes out that definition, plus it goes into the subtleties and exceptions that become second nature to geologists.
_{The mineral magnetite — Geology Guide photo}