Choose between Two Options

• $49 for one basic foot exam and x-ray ($125 value)
$29 for one medical-grade pedicure ($65 value)

Pumice Stone: Lava Spills, Pedicures, and Primordial Life

To get your feet into silky-smooth condition, the staff at nail salons use pumice stones. Learn where this unusual rock comes from with Groupon’s guide.

The dull, blue-grey color of a pumice stone belies its fiery birthplace: the belly of a volcano. As lava is ejected from inside, where temperatures can climb higher than 2,000 degrees Fahrenheit, contact with cool air and water causes it to quickly solidify into pumice. The rapid pressure and temperature changes leave small air bubbles trapped within the stone, making it buoyant—the only rock that floats, in fact (although it will take in water and sink over time, like most islands). Miners extract it for use as a building material, an additive to household cleaners, and a callus exfoliator in pedicures around the world. Pumice is also the stone that gives stone-washed denim its name. In spas, hunks of pumice are ideal for providing a rough texture without a lot of weight, making them an easy-to-use tool for pedicurists.

Though human use of pumice dates back to ancient Rome, where it was used for both construction and hair removal, its biological utility is much, much older. Because of its buoyancy, pumice stone has acted as a "raft" that can carry organisms great distances, a phenomenon documented by researchers at Queensland University of Technology after Tonga's volcanic eruptions in 2006, when pumice rafts transported about 80 marine species some 5,000 miles. Professor Martin Brasier of Oxford University made a much more dramatic assertion in 2011. He posited that the unique properties of pumice "could have made an ideal ‘floating laboratory’ for the development of the earliest microorganisms," meaning that the stone could have housed some of earth's first life forms more than 3.5 billion years ago, when the sun was still just a tiny light bulb.