Spinel Description

Pink to red spinel ring
Pink to red spinel is in high demand among gem connoisseurs. - Courtesy a Private Collector and Mona Lee Nesseth, Custom Estate Jewels
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.

Spinel crystal and cut stone
Spinel specimens range from extraordinary crystals to beautifully cut stones. - Jeffrey Scovil, courtesy Barker & Co
Spinel can also form flattened crystals that look radically different from octahedral crystals. The flattened shape occurs when the pyramids that form an octahedron rotate against each other during growth. Scientists describe this as a “twinned crystal.” Large gems cut from good-colour twinned crystals are typically shallow, and should be judged on their overall beauty rather than on proportions alone.

Fashioned and rough spinel
The fashioned spinel is from Sri Lanka, while the rough crystals are from Myanmar. The second crystal from the right is an octahedron. The other crystals rotated during growth and appear flattened. Scientists call them twinned crystals.
The spinel used in jewellery is a small part of a group of minerals that share the same crystal structure. Not all of them form transparent crystals suitable for jewellery use, however. Spinel offers a range of hues, from orange to intense “traffic light” red, vibrant pink and all shades of purple, blue and violet through to 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 colour to a mixture of iron and chromium.

Various Spinel Colors
Spinel comes in beautiful red, pink, purple and blue colours.
Violet to blue spinel can be coloured by trace amounts of iron, and vibrant blues owe their saturated colour to trace amounts of cobalt.