I think the correct term is impure (imperfect) Grossular Garnet which is a Calcium-Aluminum mineral species of Garnet but in this case, where the Cacium was partialy replaced by Ferrous Iron and the Aluminum partially replaced by Ferric Iron. Yeah, I had to look some of the information up! However, I have dug many specimens of Grossular Garnet over the years, mainly outside of Burnsville, North Carolina but also in some other areas of North Carolina and a few in Tennessee. I still have some that I have dug and one is a perfect Dodecahedron crystal about the size of a Golf ball but it is butt ugly due to the Iron composition it is partialy made up of.
Frank