Herkimer Diamond Identification Guide
A practical guide to identifying doubly terminated Herkimer quartz crystals by their clarity, 18-faced form, and host dolostone.
Read the full Herkimer Diamond encyclopedia entry →
What a Herkimer Diamond Looks Like
A "Herkimer diamond" is not a diamond at all — it is an exceptionally clear, doubly terminated quartz crystal. The name comes from Herkimer County, New York, where these crystals weather out of a hard dolostone. Their natural double points and glassy clarity make them look faceted even though they grew that way.
- Color: usually water-clear/colorless; some are smoky, included with black anthraxolite, or contain water/oil-filled cavities (enhydros).
- Luster: brilliant, vitreous to almost adamantine.
- Transparency: transparent.
- Habit: short, stubby, doubly terminated crystals with 18 faces (six prism faces plus two six-sided pyramidal terminations).
Field-ID Checklist
- Confirm the crystal has points on BOTH ends — the defining trait. Most quartz attaches to matrix and has only one termination.
- Look for glassy clarity and sharp, geometric faces.
- Check for the classic 18-face geometry (six-sided prism with two pyramidal tips).
- Look inside for tiny bubbles, black carbon inclusions, or moving water (enhydro) — common in genuine Herkimers.
- Test hardness against glass and steel.
Key Diagnostic Tests
- Mohs hardness: 7 — it easily scratches glass and a steel knife will not scratch it.
- Streak: white (but test on unglazed porcelain only on a scrap, since it is harder than the plate).
- Cleavage/fracture: no cleavage; conchoidal fracture.
- Density: ~2.65 g/cm3, typical of quartz.
- Acid/magnetism: inert; non-magnetic; no reaction to dilute acid (the host dolostone may fizz weakly).
Common Look-Alikes
- Real diamond: far harder (10), much higher dispersion/fire, and never naturally doubly terminated in this stubby quartz form. A diamond tester instantly separates them.
- Cubic zirconia / glass imitations: glass is softer (won't scratch as quartz does) and lacks natural crystal faces; CZ shows more fire.
- Ordinary quartz crystals: usually singly terminated and attached to matrix; Herkimers float free with two points.
- Tibetan/Pakistani "Herkimer-type" quartz: genuinely similar doubly terminated quartz, but only New York stones are true Herkimers — locality, not mineralogy, is the difference.
Where It Is Found
Classic sites are around Middleville, Fonda, and Little Falls in Herkimer County, New York, where crystals occur in vugs within the Cambrian Little Falls Dolostone. Collectors crack the hard rock or sift loose pocket clay. Similar doubly terminated quartz occurs worldwide, but only Herkimer County material carries the name.
Frequently asked questions
How can you tell if it is a real Herkimer diamond?
Genuine Herkimers are doubly terminated (pointed at both ends), water-clear quartz with 18 natural faces, a hardness of 7, and often tiny black carbon or water inclusions. They scratch glass easily and form free of matrix. True examples come from Herkimer County, New York.
Is a Herkimer diamond a real diamond?
No. It is a variety of quartz, not diamond. It only resembles a cut diamond because it grows with naturally faceted double terminations. Diamond is much harder (10 vs 7) and shows far more fire.
Herkimer diamond vs quartz — what is the difference?
A Herkimer diamond IS quartz, but specifically a stubby, exceptionally clear, doubly terminated crystal from Herkimer County, NY. Ordinary quartz is usually attached to rock and singly terminated.
What does a Herkimer diamond look like?
Like a small, brilliant, glass-clear crystal pointed at both ends, with sharp geometric faces and sometimes black carbon flecks or trapped water bubbles inside.
Herkimer Diamond identified by the community
Recent Herkimer Diamond specimens identified with Rock Identifier.
