Herkimer Diamond

Herkimer diamond is not a diamond but a variety of quartz (SiO₂), a naturally doubly terminated, exceptionally clear crystal named for Herkimer County, New York. Herkimer diamonds are not diamonds - they're doubly terminated quartz crystals (naturally pointed at both ends) found in dolomite rock in Herkimer County, New York. Their exceptional clarity and natural double termination make them look like faceted gems straight out of the ground, which earned them the 'diamond' trade name.

These crystals grew approximately 500 million years ago (Cambrian period) in cavities within dolostone - a magnesium-rich sedimentary rock. Unlike most quartz crystals, which grow attached to matrix with a single termination, Herkimer diamonds formed freely suspended in fluid-filled pockets, allowing them to develop terminations at both ends. The cavities also limited their growth, keeping most crystals small and concentrating their clarity.

The most prized specimens are water-clear with brilliant vitreous luster. Some contain black carbon inclusions (called 'smoky' or 'carbon Herkimers') or fluid-filled enhydro cavities visible inside the crystal. Mining is done by hand in specific quarries and road cuts in Herkimer County - you can visit and mine your own.

Herkimer diamonds are identified by their exceptional clarity, double termination (points at both ends), and brilliant vitreous luster. At hardness 7, they're standard quartz. The crystals are typically small (most under 2 cm) and remarkably clean.

Distinguish from doubly terminated quartz from other localities (marketed as 'Pakistan diamonds,' 'Tibet diamonds,' etc. - these are NOT Herkimer diamonds regardless of appearance), from actual diamond (much harder at 10, different luster), and from cut glass (no natural crystal faces, may have bubbles). True Herkimer diamonds come only from Herkimer County, NY.