If it's aluminum, then it's not a Green Monster. It's a Black Beast. However, color is not an absolute indicator, as some early aluminum versions were supposedly still painted green. Gotta' go get the bathroom scales to know for sure.
Urban legend tells the story of the reason for the transition from magnesium to aluminum. As related, supposedly the local fire marshal walked in one day, saw camera bodies being machined from solid blocks of magnesium, and the factory floors covered with large heaps of fine magnesium shavings. It's said he almost keeled over in a dead faint.
It weighs in at 18 lbs 9 oz. It's the missing link: a Green Beast.