In southwestern Arkansas, deep in the humid foothills of the Ouachita Mountains, you’ll find one of the oddest little state parks in the country. On first glance the park seems to be little more than a plowed field edged by scraggly forest, featuring a big public swimming pool and a hulking barn-like structure sheathed in rusty tin siding. You’d likely drive right past it on your way to Murfreesboro or the much more scenic canyon of the Little Missouri River, a few miles down the road.
Yet this seemingly unremarkable patch of ground was designated as one of the world’s most significant natural areas by the International Union for the Conservation of Nature. The feature that attracted the notice of the IUCN naturalists was a geological structure called a Lamprolite Pipe, a kind of subterranean chimney coursing through the upper mantel of the continent down to a seething pool of magma. Lamprolite pipes are rare things. There are only a few known to exist in North America. And these pipelines to the surface of the earth convey even rarer objects formed in the Chthonic depths: diamonds. And not just any diamonds, either: Lamprolite diamonds, prized for their size, clarity and scarcity (98 percent of the world’s diamonds are formed out of Kimberlite). Hence the name of this obscure little park: Crater of Diamonds.