How Do Spinels Form?

What is Spinel?

The term “spinel” actually describes a large group of related magnesium aluminum oxide mineral species. They’re all isometric oxides of magnesium, iron, and zinc, with traces of aluminum and other elements. However, the gemstones we typically call spinels form just a subset of this larger group.

Spinels are frequently used to simulate other more well-known or expensive gemstones, especially in birthstone jewelry. Today, many consumers are unfamiliar with spinel as a gemstone in its own right, but that’s slowly changing.

Where Do Spinels Form?

Spinels occur most commonly in magnesium-rich limestone deposits that have been subjected to contact, and sometimes regional, metamorphism. Powerful metamorphic forces convert soft limestone into harder dolomite marble. This causes the available aluminum, oxygen, and magnesium to crystallize into spinel.

Some spinel is mined directly from the primary rock where it formed. However, many secondary alluvial deposits house