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.
Brown A brown coating gives a piece of jewelry the color of chocolate (dark) or coffee (light) brown. This color of plating is not commonly seen in jewelry, and presents unique and exclusive statement pieces.