STEVE INSKEEP, host:
Much economic news is grim this summer, but not all. Parts of the upper Midwest have seen a rush for a natural resource. It's silica sand, used in fracking, a growing method for extracting natural gas. Harvest Public Media's Kathleen Masterson visited an Iowa sand mine.
KATHLEEN MASTERSON: Here in northeast Iowa, where the undulating farm fields spill into 300-foot bluffs overlooking the Mississippi River, the Pattison family ran a grain business for decades. They stored the grain in old, unused mine tunnels carved into the cliffs and loaded it onto barges to ship downriver. They pretty much ignored the sandstone all around them.
But then one day, owner Kyle Pattison got a phone call.
Mr. KYLE PATTISON (Pattison Sand Company): We decided to open up the mine because of being requested by a fracking company to. They asked us to supply sand for frack.
MASTERSON: So with a nudge from the natural gas industry, Pattison sold his grain biz and opened up Pattison Sand Company. And he's not the only one to jump into the business.
Sandstone deposits are plentiful and accessible across the upper Midwest and in Texas and Oklahoma. They're reopening or ramping up production to meet the huge demand. But why can't the natural gas industry get enough of this sand?
Mr. BILL SIMPKINS (Iowa State University Geology Professor): This sand actually has a lot of the properties that they covet. So they are descending upon all these areas to provide this particular sand unit for their shale gas fracking operations.
MASTERSON: Iowa State University geologist Bill Simpkins says the industry is using silica sand because of its unique spherical shape and incredible toughness. To extract natural gas bound up in shale rock, energy companies drill thousands of feet down and then blast pressurized water and chemicals into the shale to fracture it.
Mr. SIMPKINS: And the role of the sand is to keep the fractures open.
MASTERSON: Other materials can do the same job, but sand is the cheapest. According to U.S. Geological Survey data, production of frack sand has more than quadrupled since 2000.
Back at Pattison San Company in Iowa, business has been booming. Over the past six months, the company has hired 50 new workers. To enter the mine, you have to drive a diesel truck - because gas is too combustible - down a switchback road that winds its way to the bottom of the 300-foot bluff to an opening carved into the cliff's side.
And we're going into the south entrance of the mine. Let me put my hard hat on.
(Soundbite of machinery)
Ms. BETH REGAN (Environmental Permit Coordinator, Pattison Sand Company): These are the pillars, you know, these squares that are left in place.
MASTERSON: That's Beth Regan, the environmental permit coordinator for Pattison Sand. She points to the 55-square-foot pillars of rock the miners leave to hold up the ceiling as we drive through the crypt-like, honeycomb chambers.
Ms. REGAN: What you're hearing are the ventilation fans.
MASTERSON: After decades of using the mines just to store grain, sand is flying out the door. Pattison ships as many as 45 rail cars full of sand each day. A back-of-the-envelope calculation shows that could bring in more than $100,000 a day.
Tom Dolley of the U.S. Geological Survey says this sand fetches a much higher price when used for fracking than for construction, or even making glass bottles.
Mr. TOM DOLLEY (U.S. Geological Survey): There's considerable variation in price. But, yeah, frack is going to be over double what you would see for glass container price.
MASTERSON: In Iowa alone, the Pattison mine could easily have enough sandstone to last 10 years. That's a lot, considering that to meet fracking demand, it's running 24-7 all year long.
For NPR News, I'm Kathleen Masterson.