Scientists finally trace sapphires’ creation to fiery volcanic processes within Earth’s crust, no more than 7 kilometers below the surface.
For centuries, sapphires have captivated humanity with their deep blue allure, symbolizing purity, wisdom, and divine favor. Yet, despite their value and significance, the exact origins of these precious gems have remained a mystery, eluding scientists for generations. A recent breakthrough study has finally unraveled this enigma, revealing that sapphires are forged not in the depths of Earth’s mantle, but much closer to the surface, within the fiery turmoil of volcanic activity in the crust.
Sapphires have long been extracted from volcanic deposits, particularly those low in silicon, yet mineralogists have struggled to determine whether these gems form in the mantle or within the crust as magma ascends. The study, published in Contributions to Mineralogy and Petrology, has provided conclusive evidence that the beautiful blue sapphires originate in the upper crust, at depths of no more than 7 kilometers.
Led by researchers from the University of Heidelberg in Germany and Curtin University in Perth, Australia, the team embarked on a detailed investigation of sapphires found in the Eifel mountain range in Germany. This region, shaped by ancient volcanic activity, has been a site of mantle-derived magma intrusions into the crust for nearly 700,000 years. By analyzing over two hundred sapphires from this area using mass spectrometry, the scientists examined two key characteristics: the presence of rutile and zircon, minerals that appear during sapphire formation, and the oxygen isotope ratios in alumina, the compound from which sapphires are formed.
Their findings were striking. The sapphires were indeed formed within the Earth’s upper crust, shaped by intense heat and pressure as alumina crystallized into corundum, the primary mineral that comprises sapphires. The magmatic processes at work provided not only the heat necessary for sapphire formation but also acted as an “elevator” for these crystals, lifting them to the Earth’s surface.
“One explanation is that sapphires in the Earth’s crust originate from previously clay-rich sediments exposed to very high temperatures and pressures. The ascending magma simply acts as a transport mechanism, bringing the crystals to the surface,” explains Professor Axel Schmitt, a co-author of the study, highlighting the delicate interplay between geological forces that leads to the creation of these stunning gems.
This discovery is a significant advancement in our understanding of gemstone formation, offering new insights into the geological processes that occur near Earth’s surface. The findings not only answer a question that has puzzled scientists for years but also deepen our appreciation of the natural forces that craft such beautiful and valuable stones.
By Orlando J. Gutiérrez