This resource is mined in the Scottish village of Lochaline, which was visited by Ed Conway in the first of six parts of a 2023 book. Chinese vessels have attempted to covertly collect this resource from Taiwan’s Matsu Islands. India has violent (15[1])“mafias” that illegally export this resource, (15[1])whose mining has endangered gharials and Lake Poyang’s freshwater porpoises. Environmentalists have decried Indonesia’s massive exports to this resource’s largest importer, (*) Singapore. New Jersey has spent billions on “nourishment” projects that have replenished this resource after a 2012 natural disaster. A U.S. admiral claimed that China was making a “Great Wall” of this resource in the South China Sea as part of its reclamation (-5[1])process. This substance is dredged to manufacture concrete. For 10 points, name this silica-rich substance collected from beaches. ■END■ (10[1])