From a story on WEAU-TV, Eau Claire:
RED WING, Minn. (AP) — Under the forested bluffs of southeastern Minnesota lies an increasingly sought-after resource. It’s called “frac sand.” And it’s prized by the energy industry, which uses it to extract gas and oil from underground rock in a process called hydraulic fracturing, or fracking.
Minnesota Public Radio reports an increasing number of companies are eying Minnesota for the sand, prized for its perfectly round, hard and chemically inert grains. One energy company recently purchased land near Red Wing for sand mining, sparking opposition from residents and environmentalists.
From an article in the Star Tribune, Minneapolis-St. Paul:
The fracking process pumps a mixture of frac sand, water and chemicals into underground rock formations to break up the stone and release oil and natural gas. It allows affordable access to fossil fuel supplies that once were too expensive to tap.
But it’s been a contentious issue in some states that have fracking operations. Critics argue that chemicals used in fracking may be contaminating water supplies.