Sapphires are among the most precious gems, yet they consist solely of chemically ‘contaminated’ aluminum oxide, or corundum. It is widely assumed that these crystals with their characteristically blue color come from deep crustal rocks and accidentally ended up on the Earth’s surface as magma ascended. Geoscientists have now been able to show that the sapphire grains found in the Eifel (Germany) formed in association with volcanism.
