Sand or other proppants such as ceramic beads are vital to fracking. Sand (or a proppant) is a significant part of the mix that's injected into a well to fracture the rocks. Once a formation has been fracked, the sand props open the cracks in the rock allowing the gas to flow.
To squeeze hydrocarbons out of shale, fracking companies need to pump enormous amounts of sand and other materials into the ground. In the US fracking for shale and tight gas was expected to consume more than 43 billion kg of sand just in 2014.
In recent times (2013-2014), drillers have discovered that using much more sand than they'd previously been injecting results in higher gas production. A single fracked well can now use as much as 10,000 tons of sand.
Mega sand mines to feed the fracking industry are springing up across the US, generating their own set of impacts. As well as polluting the air, sand mines are raising fears about the potential health risks from massive quantities of airborne crystalline silica. Crystalline silica, in the form of sand, can cause silicosis - an incurable but preventable lung disease when inhaled.