What is a Herkimer Diamond? Double-Terminated Quartz from New York

What Is a Herkimer Diamond?

A Herkimer Diamond is a naturally double-terminated quartz crystal — a crystal with fully formed, faceted points at both ends — found primarily in Herkimer County, New York. They are not diamonds. They are quartz (SiO₂), chemically identical to any other quartz crystal. What makes them extraordinary is their combination of exceptional clarity, perfect natural geometry, and the remarkable geological conditions that produce their distinctive double termination.

The name "Herkimer Diamond" was given by early European settlers who were astonished by the diamond-like clarity and natural faceting of these crystals. The Mohawk people of the region had known and used them for centuries before European contact, calling them "Manitou Stones" — spirit stones.

Geological Formation: Why Only Herkimer County?

Herkimer Diamonds form in a very specific geological environment that exists in only a few places on earth — and nowhere produces them in the quality and quantity of Herkimer County, New York.

The Dolostone Host Rock

Herkimer Diamonds form within cavities (called vugs) in the Cambrian-age Little Falls Dolostone — a sedimentary rock approximately 500 million years old. This dolostone was deposited in a shallow tropical sea that covered what is now New York State during the Cambrian period.

The Formation Process

As the dolostone lithified and was buried, silica-rich fluids percolated through the rock, filling cavities. The key to Herkimer Diamond formation is the specific chemistry of these fluids and the slow, undisturbed crystallization environment within the sealed cavities:

Silica-rich hydrothermal fluids entered pre-existing cavities in the dolostone
The cavities were sealed — no external disturbance during crystallization
Crystallization proceeded extremely slowly over millions of years
Because the crystals grew freely in solution (not attached to a matrix), they developed terminations at both ends
The exceptional purity of the silica solution produced the characteristic water-clear transparency

Why Double Termination?

Most quartz crystals grow attached to a matrix (host rock) at one end, developing a termination only at the free end. Herkimer Diamonds grew freely suspended in solution within sealed cavities, allowing both ends to develop full terminations simultaneously. This is the defining characteristic — and the geological explanation for their rarity.

The Inclusions

Many Herkimer Diamonds contain inclusions of:

Anthraxolite: Black carbonaceous material (ancient petroleum) — the most common inclusion
Fluid inclusions: Tiny bubbles of ancient water or petroleum trapped during crystallization — literally 500-million-year-old water
Enhydros: Herkimers with visible moving fluid inclusions — among the most prized specimens
Phantoms: Ghost-like outlines of earlier growth stages within the crystal

Physical Properties

Chemical composition: SiO₂ (silicon dioxide) — identical to all quartz
Crystal system: Trigonal
Hardness: Mohs 7–7.5 — excellent for jewelry
Specific gravity: 2.65
Clarity: Typically water-clear to near-water-clear — exceptional for natural quartz
Terminations: Double — fully faceted points at both ends
Natural facets: 18 facets in the classic Herkimer habit (6 prism faces + 6 upper rhombohedral faces + 6 lower rhombohedral faces)

Quality Grading

Clarity

The most important quality factor. The finest Herkimer Diamonds are water-clear — completely transparent with no visible inclusions. Clarity grades:

AAA (Gem grade): Water-clear, no visible inclusions, perfect or near-perfect terminations. Suitable for fine jewelry.
AA: Near-water-clear with minor inclusions or slight cloudiness. Excellent for jewelry and display.
A: Good clarity with visible inclusions or minor cloudiness. Good for display and metaphysical use.
Included specimens: Significant inclusions — anthraxolite, fluid inclusions, or cloudiness. Valued for their inclusions rather than clarity.

Termination Quality

Both terminations should be fully formed, with clear, sharp facets. Damaged, chipped, or incomplete terminations significantly reduce value. Natural etchings and surface features are acceptable and often desirable in collector specimens.

Size

Herkimer Diamonds range from tiny (under 1cm) to exceptional specimens over 10cm. Larger, high-clarity specimens command significant premiums. Gem-quality stones over 2cm are considered exceptional.

Inclusions as Features

For collector specimens, inclusions are often desirable rather than detrimental:

Enhydros (moving fluid): The most prized inclusion type — premium specimens
Anthraxolite: Adds visual interest and geological significance
Phantoms: Beautiful and scientifically interesting
Rainbow inclusions: Internal fractures that create rainbow iridescence

Metaphysical Properties

The following reflects spiritual traditions. See our editorial policy.

Herkimer Diamonds are considered among the most powerful quartz crystals in metaphysical traditions, with properties attributed to both their exceptional clarity and their double termination:

Amplification: Said to be the most powerful amplifier of all quartz varieties — the double termination allows energy to flow in both directions simultaneously
Attunement: Traditionally used in pairs — one given to each person in a relationship to maintain energetic connection across distance
Dream work: Associated with lucid dreaming, dream recall, and accessing higher states of consciousness during sleep
Clarity and vision: The exceptional transparency is said to reflect and amplify mental clarity and clear seeing
Detoxification: Associated with clearing energetic blockages and purifying the energy field

Herkimer Diamonds in Jewelry

Herkimer Diamonds are increasingly popular in fine jewelry — their natural faceting and diamond-like clarity make them visually stunning without any cutting or polishing. They are typically set in their natural form, showcasing the crystal's geometry.

Common jewelry forms:

Pendants: The most popular format — the crystal hangs freely, catching light from all angles
Rings: Bezel settings protect the crystal's terminations; prong settings showcase the natural form
Earrings: Matched pairs of similar size and clarity
Bracelets: Smaller Herkimers set in sterling silver or gold

Browse our Herkimer Diamond collection — loose specimens and jewelry in sterling silver and gold.