Spinel, like garnet and diamond, is singly refractive, with the same physical properties in all crystal directions. It belongs to the cubic crystal system, and its characteristic crystal shape is an octahedron, which looks like two back-to-back pyramids. Well-formed spinel crystals are fairly common in nature.

The spinel used in jewelry is a small part of a group of minerals that share the same crystal structure. Not all of them form transparent crystals suitable for jewelry use, however. Spinel offers a range of hues, from orange to intense “stoplight” red, vibrant pink, and all shades of purple, blue, and violet through bluish green. Intense reds and pinks are caused by traces of chromium. The higher the chromium content, the stronger the red hue. Orange and purple stones owe their color to a mixture of iron and chromium.

The most valued spinel colors are bright red, cobalt blue, and vivid pink and orange. Pale lavender is more affordable