A crystal the size of a school bus? Dr. Michael A. Wise is a geologist, and an expert on pegmatites, at the Smithsonians National Museum of Natural History (Smithsonian Institution)
A crystal the size of a school bus?

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. It is known as "pegmatite." Unlike most rocks, pegmatites contain unusually large crystals of a wide variety of minerals.


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. That 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. It is mined from pegmatites, the only rock where it occurs in high concentrations. Spodumene is the source of high-purity lithium. That is 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."

Join us on Thursday, April 16, 2015, for a Smithsonian Science How live webcast titled Mineral Dependence - Gemstones to Cellphones. It will air at 11 a.m. and 2 p.m. EDT on the Q?rius website. Mike Wise will appear live to discuss and answer questions. Get teaching resources to support your webcast experience.

Critical thinking challenge: How are we dependent upon minerals?

Assigned 18 times

  • Adeenaz-Cla
    4/08/2015 - 06:06 p.m.

    In the story, I thought the crystal was the spodumene, but it was the pegmatites. I had gotten the answer on the quiz wrong on that question. The best part about the stories was that it was an amazing and unexpected text.A crystal as huge as a bus,that is very big. That was awsome!
    To: Ms. Clarkson. From: Adeena Zaidi

  • Hannahh-Cla
    4/08/2015 - 07:46 p.m.

    Summary-A spodumene was found. Pegmatites are igneous rocks, they are made by magma and it crystallizes to form pegmatites. They are very beautiful and are used for many products.

  • Eric0221-YYCA
    6/16/2016 - 02:37 p.m.

    The miners in South Dakota had been able to see a crystal that is the size of a school bus which had been the biggest and heaviest crystal that the miners had been able to see in South Dakota. The crystal had been able to get a lot of elements to be put together and forming a big amount of crystals from other elements. The crystal had been something that had been the biggest because of the elements that had been put in all together and making it into one big element. The minerals that had been used to make the giant crystal is that they would be able to get a lot of things that had been put together into one.
    Critical Thinking Question: How are we dependent upon minerals?
    Answer: I know that we are dependent upon minerals by using some of the minerals that are used to make things like phones or something else.

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