Bubbly Ride
How diamond surfaces
This thin slice of a kimberlite rock from northern Canada shows colorful minerals caught up in magma that rose from deep within the Earth.
Drop a Mentos candy in a bottle of Diet Coke, and carbon dioxide will bubble violently out of the soda. Similar chemical reactions may send certain kinds of magma frothing up from deep within the Earth, carrying diamonds along the way. The discovery, reported in the Jan. 19 Nature, solves several mysteries about why and how diamond-bearing rocks appear where they do. As gem-laden magma rises, the theory goes, it gobbles a mineral called orthopyroxene, changing the magma's chemical composition and belching carbon dioxide gas that drives its continued ascent. "We've provided a simple, chemically reasonable process to have dissolved gas at depth," says Kelly Russell, lead author of the new paper and a volcanologist at the University of British Columbia in Vancouver. Diamond mines tap volcanic rocks called kimberlites, which contain many kinds of crystals that must have formed at high pressures 150 kilometers or more deep, in the planetary layer known as the mantle. How those mantle crystals make it to the surface has been a puzzle, since magma gets denser the more crystals it picks up. Most geologists have assumed that the magma must bubble gases to keep it moving up, but no one has been able to explain exactly how.
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