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.
Tiger's Eye is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown color, with a silky luster. Its hardness on the Mohs scale is 5.5-6, and its specific gravity is 2.64-2.71.