Yes, sand. And more specifically sand mining. The Wilmington Star-News offers up a fascinating look a this obscure but critical business:
For most people, sand mining is an invisible step in the construction process. The mining is typically tucked away in industrial corridors, and the sand is used in construction projects long before the first viewing of a building takes shape, keeping sand mines out of sight and out of mind.
But as the need for sand in local construction projects increases and suitable land grows scarce, concerns over sand mining are creeping into the limelight.
About 30 sand mining sites have been approved in [New Hanover County] by the N.C. Department of Environment and Natural Resources in the past 50 years, with 10 of these considered active sand mines. And this could just be the tip of the iceberg. There could be far more unlisted operational sand mines located throughout the county, thanks to loopholes in NCDENR’s rules.