Citrine is a variety of quartz whose color ranges from a pale yellow to brown due to ferric impurities. Natural citrines are rare, and most commercial citrines are heat-treated amethysts or smoky quartzes.
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.