Visitors break apart exposed dolostone to search for naturally double-terminated quartz crystals known as Herkimer diamonds, which formed roughly 500 million years ago. The fee-dig surface mine operates seasonally and provides basic tools and instruction, with anything found by visitors theirs to keep.
Filed under roadside oddities: giant objects, odd monuments and things built for no clear reason.
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Source: herkimerdiamond.com/mine/