Unveiling the Mystery: How “Contaminated” Aluminum Oxide Turns Into Precious Sapphires

Researchers at Heidelberg University are investigating how this distinctively blue-colored crystal forms in volcanic melts.
Sapphires, highly valued as precious gems, are essentially aluminum oxide, or corundum, with chemical impurities. These typically blue crystals are predominantly found in silicon-poor volcanic rocks worldwide. It is widely believed that sapphires form in deep crustal rocks and are transported to the Earth’s surface by ascending magma. Geoscientists at Heidelberg University, through geochemical analyses, have demonstrated that the millimeter-sized sapphire grains discovered in the Eifel region of Germany formed in conjunction with volcanic activity.

The Eifel is a volcanic region in the center of Europe where magma from the Earth’s mantle has been penetrating the overlying crust for nearly 700,000 years. The melts are poor in silicon dioxide but rich in sodium and potassium. Magmas similar in composition worldwide are known for their abundance of sapphire.