Sapphires form inside the fiery hearts of volcanoes, not deep in the mantle like we thought | Live Science
Planet Earth Geology Sapphires form inside the fiery hearts of volcanoes, not deep in the mantle like we thought News By Stephanie Pappas published 6 August 2024 A new study of sapphires found in volcanic fields in Germany reveals that these beautiful blue stones form where magma and rocks from Earth’s crust mix.
When you purchase through links on our site, we may earn an affiliate commission. Here’s how it works .
A sapphire from sediment in the Kyll, a river in the western Eifel. The crystal measures approximately 0.9 mm in diameter. (Image credit: © Sebastian Schmidt) Brilliant-blue sapphires look like bits of sky brought down to Earth — but a new study finds these gemstones are from a different boundary: the one between the planet’s crust and magma welling up from the mantle, Earth’s middle layer.
Sapphires have been thought to form in the mantle itself or in the lower sections of the crust, study senior author Axel Schmitt , a geologist at Curtin University in Australia who conducted the work while at Heidelberg University in Germany, told Live Science. But the new research finds that, instead, sapphires are born higher in the crust, in the hearts of volcanoes where magma rises to only about 3 miles (5 kilometers) below the surface.
“We can pinpoint this region as the ‘crucible’ where sapphire formed,” Schmitt said.
Gem-quality sapphires typically come from placer deposits, which are river sediments that wash minerals out of their original source rock. Without those source rocks, it’s tough to get information on how the gems formed. Schmitt and his colleagues turned to the Eifel formation in western Germany, which was created by volcanoes over a long period stretching from the Cretaceous period (145 million to 65 million years ago) to the most recent eruption 13,000 years ago.
“The Eifel volcanic field shares many similarities with basaltic volcanic fields that are often identified as the sources for sapphire placer deposits,” Schmitt said. “However, it is much younger,” making it a promising place to investigate the chemistry and age of sapphires found there.
Sapphires are made of the mineral corundum, which is made mostly of pure aluminum and oxygen. But the stones also contain imperfections called inclusions, which are incorporated into the gem when it forms. Using ratios of radioactive uranium and lead in these inclusions, the researchers determined the ages of the sapphires. The team also looked at different versions of oxygen in the sapphires, which reveal where the chemical building blocks of the sapphires came from. They studied 223 tiny sapphire grains, which were not gem-quality.
Together, these trace elements revealed that the sapphires formed less than 2.5 million years ago, meaning they formed in the tail end of the volcanic activity that formed the Eifel field. Their oxygen molecules were similar to those found in magmas brought to the surface, Schmitt said. This meant the sapphires formed at the boundary between surface rock — the crust — and magma.
Sign up for the Live Science daily newsletter now Get the world’s most fascinating discoveries delivered straight to your inbox.
Contact me with news and offers from other Future brands Receive email from us on behalf of our trusted partners or sponsors By submitting your information you agree to the Terms & Conditions and Privacy Policy and are aged 16 or over. RELATED STORIES — See the ‘Star of India,’ decades after it was nabbed in a heist
— Why is the color blue so rare in nature?
— Next-gen quantum computers could be powered with sapphire lasers
“The likely environment for this is the edge of a subsurface magma intrusion, where the surrounding rocks are heated, melted and intermingled in contact with magma,” Schmitt said.
Because the researchers knew the depth of the magma in the Eifel field, they were able to pin down this formation depth to between 3.1 and 4.3 miles (5 and 7 km). Schmitt’s next goal is to find mineral “fingerprints” that will help determine the origins of sapphires as a way to trace gemstone supply chains and ensure ethical business practices, particularly because many sapphires are mined in developing countries where environmental regulation and human rights protections are not always stringent.
While sapphires have not been known to fuel and fund conflict in the same way as “blood diamonds,” there have been occasional allegations of human right abuses by gemstone mining companies .
Stephanie Pappas Social Links Navigation
Live Science Contributor Stephanie Pappas is a contributing writer for Live Science, covering topics ranging from geoscience to archaeology to the human brain and behavior. She was previously a senior writer for Live Science but is now a freelancer based in Denver, Colorado, and regularly contributes to Scientific American and The Monitor, the monthly magazine of the American Psychological Association. Stephanie received a bachelor’s degree in psychology from the University of South Carolina and a graduate certificate in science communication from the University of California, Santa Cruz.
More about geology
Salar de Uyuni: The world’s largest salt desert and lithium reservoir surrounded by volcanoes
World’s largest iron ore deposits formed over 1 billion years ago in supercontinent breakup
Latest
32 of the most venomous animals in the world
See more latest ► Most Popular
Space photo of the week: A cosmic butterfly emerges from a star’s violent death
‘Love hormone’ oxytocin may be missing link between sleep apnea and high blood pressure
What were the first animals to have sex?
The building blocks of life can form rapidly around young stars
Group of ancient stars spotted near the sun could rewrite the Milky Way’s history
Pacific geoduck: The large, phallic clam that can live longer than 165 years
Here’s what the 2024 Summer Olympics in Paris look like from space (photos)
How many galaxies are in the universe?
3 remarkable trees: A living fossil, a deadly canopy, and the world’s biggest seeds that were once mounted in gold by royals
These 17th-century drawings of the sun by Kepler add fire to solar cycle mystery
Pot overflowing with gold coins discovered in ancient Greek city in Turkey MOST READ MOST SHARED
1 James Webb Space Telescope spies strange shapes above Jupiter’s Great Red Spot 2 What defines a species? Inside the fierce debate that’s rocking biology to its core 3 Newly discovered asteroid larger than the Great Pyramid of Giza will zoom between Earth and the moon on Saturday 4 China opens Chang’e 6 return capsule containing samples from moon’s far side 5 Neanderthals cared for 6-year-old with Down syndrome, fossil find reveals
1 Newly discovered asteroid larger than the Great Pyramid of Giza will zoom between Earth and the moon on Saturday 2 2,000 years ago, a bridge in Switzerland collapsed on top of Celtic sacrifice victims, new study suggests 3 Self-healing ‘living skin’ can make robots more humanlike — and it looks just as creepy as you’d expect 4 Tasselled wobbegong: The master of disguise that can eat a shark almost as big as itself 5 This robot could leap higher than the Statue of Liberty — if we ever build it properly
