Spinel is the magnesium aluminum member of the larger spinel group of minerals. Its hardness is 8, its specific gravity is 3.5–4.1, and it is transparent to opaque with a vitreous to dull luster. It may be colorless, but is usually various shades of red, blue, green, yellow, brown, or black.
Hematite also spelled as haematite, is the mineral form of iron (III) oxide (Fe2O3). It forms a complete solid solution at temperatures above 950 °C (1,740 °F). Hematite is a mineral, colored black to steel or silver-gray, brown to reddish brown, or red. Huge deposits of hematite are found in banded iron formations. Gray hematite is typically found in places that can have still standing water or mineral hot springs. Hematite can also occur without water, however, usually as the result of volcanic activity.