Herkimer Diamonds

Herkimer Diamond Crystals

Herkimer diamonds are not diamonds at all — they are doubly-terminated quartz crystals (SiO₂) found in exposed dolostone outcrops in and around Herkimer County, New York. What sets them apart is their natural geometry: unlike most quartz, which grows attached to a matrix and terminates on one end, Herkimer diamonds form freely in solution cavities, producing two naturally faceted terminations and exceptional water-clear transparency. They formed roughly 500 million years ago during the Cambrian period.

Single-terminated crystals display the classic Herkimer brilliance — clean faces, sharp edges, and glass-like clarity. Double clusters feature multiple crystals growing from a shared pocket. Matrix specimens show crystals still seated in their original dolomite host rock. Some pieces contain inclusions of anthraxolite (black carbon) or fluid-filled enhydro pockets, adding significant collector interest.

Browse related quartz varieties in our Clear Quartz and Himalayan Quartz collections. For other collector-grade specimens, see One-of-a-Kind Crystals and Collector's Edition. See also our Crystals from USA collection. Free shipping on orders $150+.

Frequently Asked Questions

Are Herkimer diamonds real diamonds?

No. Herkimer diamonds are doubly-terminated quartz crystals (silicon dioxide, SiO₂) — not carbon diamonds. The name comes from their exceptional clarity and natural double terminations that give them a diamond-like brilliance. They rate 7 on the Mohs scale versus 10 for true diamond.

Where are Herkimer diamonds found?

True Herkimer diamonds come exclusively from Herkimer County and surrounding areas in New York State. They form in dolostone (dolomitic limestone) outcrops that are roughly 500 million years old. Similar doubly-terminated quartz from other locations is not technically "Herkimer diamond."

Why are Herkimer diamonds doubly terminated?

Unlike most quartz that grows attached to a rock wall, Herkimer diamonds grew freely within solution cavities in dolostone. Without attachment to a surface, the crystal could develop natural faces on both ends, creating the characteristic double termination.

What are enhydro Herkimer diamonds?

Enhydro Herkimer diamonds contain tiny pockets of ancient water (and sometimes a gas bubble) trapped inside the crystal during formation 500 million years ago. These are highly prized by collectors — some contain visible moving bubbles when tilted.

How do I identify a genuine Herkimer diamond?

Genuine Herkimer diamonds have natural double terminations, exceptional clarity, and typically show 18 natural crystal faces (6 on each termination, 6 on the prism). They often contain small black anthraxolite inclusions. They are harder than glass (Mohs 7) and will scratch glass easily.