The earth grows nice gems in minutes

Rome was not built in a day, but had some of the finest gems on Earth, according to new research from Rice University.

There are aquamarine, sapphire, garnet, zircon, and topaz, but some crystalline minerals are found mostly in pegmatites, vein-like forms that usually contain both large crystals and hard-to-find elements such as tantalum and niobium. Another common discovery is lithium, an important component of electric car batteries.

“It’s a step towards understanding how the earth concentrates lithium in certain places and minerals,” said Patrick Phelps, a rice graduate student and co-author of a study published online. Nature Communications. “If we can understand the basics of pegmatite growth rate, it is a step towards understanding the whole picture of how and where it forms.”

Pegmatites form when rising magma cools inside the earth, and it exhibits some large crystals of the earth. The Atta mine in South Dakota, for example, features log-sized crystals of lithium-rich spodumin, with an estimated tonnage weight of 42 tons and a length of 42૨ feet. Research by Phelps, Sin-Tie Lee of Rice, and Douglas Morton, a geographer from Southern California, attempts to answer the question of long-suffering psychologists: How could pegmatite contain such large crystals?

“In magmatic minerals, crystal size is traditionally associated with cooling time,” said Lee, chairman of the Department of Rice Earth, Environmental and Eclipse and Harry Carriers Wis Professor of Rice and Chairman of Rice. “The idea is that larger crystals take longer to grow.”

Magma that cools rapidly, like a rock in an erupting lava, contains microscopic crystals, for example. But the same magma, if cooled for thousands of years, could contain centimeter-sized crystals, Lee said.

“Pegmatites cool relatively quickly, sometimes in just a few years, and yet they show some of the largest crystals on Earth.” “The big question really is, ‘How can that be?'”

When Phelps began research, his most urgent questions were about how to create a set of criteria that Lee, Lee, and Morton could answer the big question.

“It was one more question, ‘Can we know how fast they really grow?'” Phelps said. “Can we use trace elements – elements that are not in quartz crystals – to find the growth rate?”

It took more than three years, a field trip to collect sample crystals from a pegmatite mine in Southern California, chemical composition maps of hundreds of lab-sized samples, and some 0-year-old physics papers into a deep dive into a mathematical model. Could.

“We examined crystals half an inch wide and more than an inch long,” Phelps said. “We showed it grown in a few hours, and there’s nothing to suggest that physics would be different in large crystals that measure one meter or more in length. Depending on what we found, larger crystals like that could grow. Day.”

Pegmatites form where pieces of the earth’s crust are pulled down and re-led into the earth’s molten mantle. Any water that is trapped in the crust becomes part of the melt, and as it melts and cools, it gives birth to many types of minerals. Each form and characteristic prevents it from melting at temperature and pressure. But water is left, cooling makes a gradual high percentage of melting.

“Ultimately, you’ll be left with so much water that it becomes more of a water-influenced liquid than a melt-dominated liquid,” Phelps said. “The remaining elements in this aqueous mixture can now move much faster. Chemical diffusion rates are much faster in liquids and liquids flow faster. So when the crystal starts to form, the elements can get to it faster, which means it Can develop quickly. “

Crystals are commanded to arrange atoms. They form when molecules naturally fall into an aligned pattern based on their chemical properties and energy levels. For example, in the mine where Phelps collected his quartz samples, cracks opened up when many crystals formed pegmatite.

“You’ll see this pop up and go through the layers of pegmatite, almost like the veins inside a vein,” Phelps said. “When those cracks opened, he quickly reduced the pressure. So the liquid rushed in, as everything expanded, and the pressure dropped dramatically. Suddenly, all the dissolved elements are now confused. They don’t want to be. They’re in a physical state now. , And they quickly begin to come together in crystals. “

To illustrate how sample crystals grew rapidly, Phelps used both cathodoluminescence microscopy and laser ablation with mass spectrometry to measure the exact amount of trace elements involved in the crystal matrix at dozens of points during growth. From the experimental work done by material scientists in the mid-20th century, Phelps was able to explain the growth rate from these profiles.

“There are three variants,” he said. “Things are likely to be brought. That’s the partition coefficient. There’s how fast the crystal is growing, the growth rate. And then there’s the difference, so how fast the basic nutrients are brought into the crystal.”

Phelps said the rapid growth rate is quite surprising.

“Pegmatites are very short-lived, so we know they have to grow relatively quickly.” “But we’re showing that it was a few orders of magnitude higher than anyone had predicted.

“When I finally got one of these numbers, I remembered going to Sin-Tiny’s office fee, and said, ‘Is this possible? I don’t think this is right.’ “Phelps recalled.” Because in my mind, I was still thinking about the millennial time standard. And these numbers meant days or hours.

“And Sin-tie said, ‘Well, why not? Why can’t it be done right?'” Phelps said. “Because we’ve done math and physics. That part was good. When we didn’t expect it to be fast, we couldn’t come up with a reason why it doesn’t make sense.”