It also occurs as a primary mineral in rare mafic igneous rocks; in these igneous rocks, the magmas are relatively deficient in alkalis relative to aluminium, and aluminium oxide may form as the mineral corundum or may combine with magnesia to form spinel. This is why spinel and ruby are often found together.

Are spinels man made?

Man-made spinel is used extensively. Discovered accidentally when scientists were experimenting to try and produce a flame-fusion blue synthetic sapphire, spinel's great advantage is that it can be made to reproduce almost all colors except purple.

Is spinel a real gemstone?

Spinel belongs to the cubic crystal system and its characteristic crystal shape is an octahedron, which looks like two back-to-back pyramids. Like ruby, spinel is found in alluvial deposits; it ranks 8 on the Mohs scale and has good toughness, making it a durable gem for jewelry.