Herkimer diamonds are not real diamonds, but a specific variety of quartz crystal. The quartz stones are double-pointed and are mined from several locations in Herkimer County in New York. Prized as a special quartz crystal due to several distinguishing characteristics including a high degree of clarity, Herkimer diamonds are collected as unusual gems and used in jewelry.
Diamonds are composed of carbon and are the hardest stones found in nature (a perfect 10 on the Mohs scale of hardness). Herkimer diamonds are actually clear quartz crystals. Their primary visual marker is that they are double-terminated, meaning that the crystal comes to a point at each end. This double-pointed quality is rare, as it indicates that there was little or no contact between the forming crystal and the host rock.
Herkimer diamonds are mined from the Little Falls Dolostone, the host rock. The Little Falls Dolostone was formed in the Cambrian era approximately 500 million years ago, and Herkimer diamonds developed in cavities in the rock, along with drusy quartz crystals and tarry hydrocarbon. The cavities are discovered by breaking the rock open. The Mohawk tribe and early North American settlers discovered Herkimer diamonds in streams and fields and prized them for their striking appearance.
Although similar double-terminated quartz crystals have been found in Arizona, Afghanistan, Norway, China and the Ukraine as well as in other locations, authentic Herkimer diamonds are mined in a single location: Herkimer County in central New York. Prime Herkimer diamond mining areas are found along New York State Route 28, in and around Middleville, New York. Additional nearby locations for double-terminated quartz crystals include Montgomery County and Warren County in New York.
Herkimer diamonds can be mined by hitting the dolomite host rock with a heavy hammer. Safety goggles and gloves are recommended, as are long pants and long-sleeved shirts, as dolomite can break into small pieces. At least two commercial Herkimer diamond mines offer tours and opportunities to prospect for Herkimer diamonds: the Ace of Diamonds Mine in Middleville, New York, and the Herkimer Diamond Mines in Herkimer, New York.
