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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. They 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 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. That is 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. It's 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?
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