Where Jewels Come From

The New York Times has an interesting article on how gems tell us “important things about the planet.”

Every gem fixed to every ring or necklace was forged deep inside our planet, according to its own recipe of elements, temperature and pressure.

In the journal Geology, Dr. Harlow — writing with Robert J. Stern of the University of Texas at Dallas, Tatsuki Tsujimori of Okayama University in Japan and Lee A. Groat of the University of British Columbia — explores some stories that gems like jade can tell. Each is different. While jade is produced from dying oceans, for example, rubies are forged in newborn mountains.

Continents are ringed by rocks like shale, formed from sediments washing off of land. When crushed in this subterranean forge, shale can produce crystals of aluminum and oxygen.

If these crystals stop developing, they become sapphires. But the crystals may instead get pushed up toward the surface of the Earth. The overlying rock they move into is rich in chromium. The chromium atoms push the aluminum atoms out of the crystals and take their place, giving them a red color. “When they get a little chromium in them, we call them rubies,” Dr. Stern said.

I’ve posted the entire article under the Science tab for those who are inerested.