Black Spinel 4mm Faceted Coin - 15-16 Inch Specimens which means

which means

Blue Tourmaline ranges in color from green to blue to yellow to green with black

Like all other natural turquoise

a banded Chalcedony that is predominantly white with layers of brown

It features:

Black Spinel 4mm Faceted Coin - 15-16 Inch Specimens which meansSpinel is a hard vitreous magnesium aluminum oxide, and comes in a range of other colors, but those varieties are transparent. Black Spinel not only has the dark color, but it is opaque as well, rendering its black especially deep and mysterious. Sometimes called the "Black Prince's Ruby" for its role in the English crown. It has been mistaken for ruby and sapphire at times, but can be distinguished by its structure and its lower relative hardness.