Jewel Cave in South Dakota is named for crystals of calcite.
The cave’s walls contain abundant sparkling calcite crystals, which inspired its “Jewel” name. Calcite is a crystalline form of calcium carbonate and is also the principal mineral in the limestone through which much of the cave developed.
Jewel Cave is protected as Jewel Cave National Monument in the Black Hills of South Dakota. It is a solutional cave: slightly acidic groundwater dissolved passages through limestone over very long periods, after which mineral-rich water deposited formations such as crystals, flowstone, stalactites, and stalagmites.
The name can cause confusion because quartz is also famous for clear, glittering crystals, but quartz is not the mineral that gave Jewel Cave its name. Nor is the cave named for precious gemstones. Its “jewels” are natural calcite crystals lining parts of the underground passages. The monument is also notable for its immense mapped extent, with hundreds of kilometres of surveyed passageways.