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The Q? Blog

A Crystal the Size of a School Bus?!

by Devin Reese -- Apr 1, 2015
Devin Reese, smiling

Devin is the lead digital science writer for the Q?rius website. She writes and gathers media for the Smithsonian Science How? webcast series,...

Blue beryl that crystallized as a 6-sided hexagonal crystal, not bus-sized but beautiful. Photo by Chip Clark, Smithsonian.
Blue beryl that crystallized as a 6-sided hexagonal crystal, not bus-sized but beautiful. Photo by Chip Clark, Smithsonian.

In South Dakota miners found a crystal of a mineral called spodumene that was 42 feet long and weighed 90 tons. While it's an extreme example, the massive crystal showcased one of the incredible qualities of the rock in which it was found, known as "pegmatite." Unlike most rocks, pegmatites contain unusually large crystals of a wide variety of minerals.

Why? Pegmatites are igneous rocks that form as melted materials (magma) cool beneath the Earth's crust. Superheated water in the magma helps some chemical elements accumulate and allows the magma to crystallize many kinds of minerals, some of which are not found in most common rock types. Miners look to pegmatites for the beryl crystals that are cut into the gem aquamarine, the spodumene for kunzite, and the spectacular and colorful tourmaline.

But pegmatites produce more than just beautiful gemstones. Many minerals valued for industrial and commercial purposes are also found in pegmatites. Consider that your cellphone wouldn't work properly without the rare element tantalum that is mined from pegmatites, the only rock where it occurs in high concentrations. Spodumene is the source of high-purity lithium required for making rechargeable batteries used in electronics. The muscovite found in mica-rich pegmatites is used in many products, including cosmetics.

Find out more about why Smithsonian Geologist Dr. Michael Wise calls pegmatites "Nature's Giant Treasure Chests." Watch a “Smithsonian Science How” webcast video titled Mineral Dependence - Gemstones to Cellphones, in which Mike discusses pegmatites and answers questions. Get teaching resources to support your webcast experience.

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