One indispensible condition for being a materialist is a failure to give any adequate account for what material is. The term is rarely defined, and when it is it is defined poorly. If, for example, one says material is any extended thing, then what are building materials? Extended buildings? What are course materials? Things that extend class? Similar arguments apply to calling material “what has mass” or any other such thing.
We call something material for its being what the Medivals called an “id ex quo”, a that from which or a that out of which something is made. Course materials are things that a course is made out of, building materials are things buildings are made from. Material is a certain principle which by nature is ordered to something else as its end and form, a building for example, or the end of a course. As material, moreover, the thing can’t account for why it moved to this end or term at all- this requires some action of a thing other than the matter. The case is no different for natural things, even the atom, is that from which something is made, insofar as we are considering it as matter.