Emily Chan
They decided to test the theory through a series of geochemical analyses, which showed that a portion of tiny sapphire grains were present in rock samples collected from volcanic deposits in the region. But most of the sapphires came from river sediments.
“Like gold, sapphire is very weathering-resistant compared to other minerals. Over protracted time periods, the grains are washed out of the rock and deposited in rivers,” Sebastian Schmidt, a graduate student at Heidelburg University, explained.
“Because of their high density, they are easy to separate from lighter sediment components using a gold pan.”
The age of the sapphires from the Eifel was determined using oxygen isotope and trace element analysis, revealing that they had been formed at the same time as volcanism.
As a result, the sapphires inherited the isotopic signature from mantle melts. They were mixed with heated and partially melted rock from the crust located about three to four miles deep.
Other sapphires were formed when they came into contact with subterranean rock walls, triggering the production of sapphires.
“In the Eifel, both magmatic and metamorphic processes, in which temperature changed the original rock, played a role in the crystallization of sapphires,” concluded Schmidt.
The details of the findings were published in the journal Contributions to Mineralogy and Petrology.
