... spinel (Transparent Magnesium Aluminate spinel, MgAl2O4 transparent spinel, MA polycrystalline spinel) is a Transparent Ceramic spinelIntrodctionTransparent ceramic spinel (Transparent Magnesium Aluminate spinel, MgAl2O4 transparent spinel, MA polycrystalline spinel ... is red, green, blue, purple, brown, and black; but red is ... faceted in oval, round, or cushion shapes and is not currently found ...