Hey Stow! Been a while. Why do you question the legality? This seems to address concentrates pretty clearly, what's your opinion? Is this contradicted somewhere else?
"Marihuana" means all parts of the plant Cannabis sativa L., growing or not; the seeds of that plant; the
resin extracted from any part of the plant; and every compound, manufacture, salt, derivative, mixture, or preparation of the plant or its seeds or
resin. Marihuana does not include the mature stalks of the plant, fiber produced from the stalks, oil or cake made from the seeds of the plant, any other compound, manufacture, salt, derivative, mixture, or preparation of the mature stalks, except the
resin extracted from those stalks, fiber, oil, or cake, or any sterilized seed of the plant that is incapable of germination. Marihuana does not include industrial hemp grown or cultivated, or both, for research purposes under the industrial hemp research act.
Source:
http://www.legislature.mi.gov/(S(z4nowemfcccwfpvw00hjkgin))/mileg.aspx?page=getobject&objectname=mcl-333-7106&query=on&highlight=resin