Herkimer diamond: a double-terminated quartz, meaning and choice

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The Herkimer 'diamond' is not a diamond: it is a clear double-pointed quartz crystal that formed in the dolostone of New York State. Origin, care, imitations.

Key points

Colour	colourless to very slightly smoky, sometimes with black inclusions
Mineral family	quartz (rock crystal), SiO2
Hardness (Mohs)	7
Form	double-pointed crystal (doubly terminated), 18 faces, naturally clear
Type locality	Herkimer County and the Mohawk Valley, New York State (USA)
Host rock	dolostone of the Little Falls Formation, Cambrian in age
Age of the quartz	debated; younger than the host rock according to some sources
Traditional correspondences	crown and third-eye chakras, depending on the authors

What is a Herkimer diamond?

Despite its name, the 'Herkimer diamond' has nothing to do with diamond: it is a quartz crystal (see rock crystal), with the formula SiO2 and a hardness of 7. Its nickname comes from its clarity and the sharpness of its faces, which evoke a cut stone. It is described as doubly terminated: it has a point at each end, whereas most quartz is attached to the rock at one end.

The first crystals were found in outcrops of dolostone in Herkimer County and the Mohawk Valley, in New York State, notably at Middleville and Little Falls, hence the names 'Middleville diamonds' or 'Little Falls diamonds'. The host rock, a dolostone of the Little Falls Formation, dates from the Cambrian (about 500 million years ago). The quartz itself formed in cavities in the rock (called vugs) much later; its exact age is debated, and some sources attribute it to the Carboniferous.

Slow growth in rock buried under sediment explains the clarity of these crystals.

Inclusions: a treasure and a signature

Many Herkimer diamonds contain small inclusions: bubbles of salt water, of carbon dioxide, and above all a solid, black hydrocarbon, which is the most frequent inclusion in these crystals. Collectors sometimes call this material 'anthraxolite', a term some sources avoid. These inclusions remind us that the crystal grew in a rock through which fluids rich in organic matter circulated.

They are also a sign of authenticity: a crystal without inclusions is entirely possible, but cut glass never contains inclusions of this kind.

'Diamonds' from other countries

Double-terminated quartz crystals are found in other regions of the world and are often sold under the name 'Herkimer'. In principle the name should refer only to crystals from New York, but one also sees 'Maramureş' stones or 'Marmarosh diamonds' (Ukrainian Carpathians) and 'Cape May diamonds' (water-worn quartz pebbles). These stones are genuine clear quartz, sometimes very similar, but their origin is different.

If a specific origin matters to you, ask for the locality. A low price for a large size is often a sign of a crystal from another region.

Traditional symbolism

In crystal literature, the Herkimer diamond is linked with clarity, lucidity and light. It is presented as a stone for contemplation, often worn as a pendant.

This symbolism is very recent: the trade in these crystals as 'energy' stones dates from the late 20th century. It draws on that of colourless quartz, which is far older (the Greeks believed rock crystal was hardened ice, hence the word krystallos). No study shows any effect on health, mood or luck.

Traditional correspondences

Area	Cited correspondence
Chakra	crown and third eye
Element	air or water
Signs	no consensus (Aquarius, sometimes Gemini)
Keywords	clarity, light, lucidity

See the crown chakra to place this association.

How to use it

As a pendant or ring: the raw crystal, set with its two points, is the most common piece of jewellery. With a hardness of 7, it copes with everyday wear (see the jewellery guide).
As a pocket stone: one point to hold in the hand.
As decoration: a few crystals in a bowl or on a windowsill.
As a point of calm: turn the crystal in the light while breathing slowly (tutorial).

Care and purification

Cleaning: lukewarm water, mild soap, a soft brush. Quartz is stable.
Sun: harmless for colourless quartz.
Salt: no risk to the stone; rinse with clear water.
Knocks: the points can chip; store crystals separately.
Smoke, sound: see the guide.

Recognising a real crystal

Cut glass: perfectly regular, often without any trace of growth, and warmer to the touch than quartz.
Reconstituted or heated quartz: small crystals of identical shape are suspect.
Genuine stone: small surface irregularities (striations, tiny steps), inclusions, slightly uneven faces.
Aura: 'rainbow' or coloured Herkimers have received a metal coating (see angel aura).

How to choose

Look for clarity and sharp points. Small crystals are affordable; large pieces that are very clear and of certified origin become noticeably more expensive. A Herkimer diamond is in any case far from the price of a real diamond. To pair it, try smoky quartz or amethyst.