Oct. 7 (UPI) — Scientists have gained new insights into crystal growth rates inside pegmatites, veinlike formations that host some of the planet’s biggest crystals, as well as valuable elements such as tantalum, niobium and lithium.
Magma cooling time typically controls the size of crystals — when magma cools quickly, crystals remain microscopic, and when it cools slowly, crystals have time to grow.
But pegmatite crystals appear to upend this logic, researchers said in a study published this week in the journal Nature Communications.
“Pegmatites cool relatively quickly, sometimes in just a few years, and yet they feature some of the largest crystals on Earth,” Cin-Ty Lee, professor of geology at Rice University, said in a news release. “The big question is really, ‘How can that be?'”
To determine the growth rates of pegmatite crystals, scientists turned to the rare elements that are often found inside pegmatites.
“It was more a question of, ‘Can we figure out how fast they actually grow?'” said Rice graduate student Patrick Phelps. “Can we use trace elements — elements that don’t belong in quartz crystals — to figure out the growth rate?”
After surveying dozens of scientific papers on the chemistry of crystal formation and closely examining a variety of crystals from a pegmatite mine in Southern California, researchers developed a formula for translating chemical profiles into crystal growth rates.
“We examined crystals that were half an inch wide and over an inch long,” Phelps said. “We showed those grew in a matter of hours, and there is nothing to suggest the physics would be different in larger crystals that measure a meter or more in length. Based on what we found, larger crystals like that could grow in a matter of days.”
Pegmatites are formed when pieces of Earth’s crust are pulled down