Short answer: a Herkimer diamond is not a diamond. It is a naturally faceted, double-terminated quartz crystal, pointed at both ends, found in cavities in dolomite rock in and around Herkimer County, New York. The "diamond" in the name comes from the crystals' exceptional clarity and well-formed faces. They rate 7 on the Mohs scale, like all quartz. You can dig for your own at fee-based mines near Middleville, New York.
What is a Herkimer diamond?
Herkimer diamonds are double-terminated quartz crystals, silicon dioxide, with a point at each end instead of one end attached to rock. They are found in exposed outcrops of dolomite in and around Herkimer County and the Mohawk River Valley. Because early discovery sites were in the village of Middleville and the city of Little Falls, they are also called Middleville diamonds or Little Falls diamonds.
Their clarity and naturally glassy faces make them look as though they have already been cut. They range in color from colorless to smoky, and in size from a couple of millimeters to more than 20 centimeters.
Are Herkimer diamonds real diamonds?
No. Diamond is carbon and rates 10 on the Mohs scale. Herkimer diamonds are quartz, silicon dioxide, at 7. The name is a nickname for their brilliance and natural faceting.
They are not the only quartz "diamonds" in the United States. Cape May diamonds are quartz pebbles found on the beaches of Cape May Point, New Jersey, most abundantly at Higbee and Sunset beaches. Unlike Herkimers, they are rounded by water rather than naturally faceted, and they are sometimes cut and polished to resemble diamonds and sold locally as souvenirs.
Herkimer diamonds vs clear quartz points
Most clear quartz points sold in crystal shops grew attached to rock at one end, so they have a single point and a rough or broken base. Herkimer diamonds grew in open cavities and finished with a point at each end. Their faces are naturally bright and glassy, so they are prized as natural crystals, while they also occur in a wide range of crystal forms, singly, as doubles and in clusters.
How did Herkimer diamonds form?
Their story began about 500 million years ago in a shallow sea, which received sediments from the ancient Adirondack Mountains to the north. Calcium and magnesium carbonate sediments built up and hardened into the dolomite bedrock now known as the Little Falls Formation, formerly the Little Falls Dolostone.
While the rock was buried, acidic water dissolved cavities, called vugs, in it. The dolomite is Cambrian in age, but the quartz in the vugs is thought to have formed much later, in the Carboniferous Period. As the rock was buried deeper and temperatures rose, crystals grew in the cavities very slowly. That slow growth produced quartz crystals of exceptional clarity.
What is inside a Herkimer diamond?
Many Herkimer diamonds contain inclusions that record how they formed:
- Solids: a black hydrocarbon is the most common solid inclusion. When abundant as tiny particles, it can give crystals a smoky color. Calcite, dolomite and pyrite also occur.
- Liquids: salt water and petroleum.
- Gases: most often carbon dioxide.
- Multi-phase inclusions, combining a bubble, liquid and solid, and negative crystals, crystal-shaped cavities inside the quartz.
Where can you dig for Herkimer diamonds?
Some of the best places to find them are along New York State Routes 28 and 29 near Middleville. Commercial mines there, including Ace of Diamonds Mine, Herkimer Diamond Mines and Crystal Grove Diamond Mine and Campground, let visitors prospect for a fee and rent tools such as rock hammers and wedges.
Crystals grow in cavities in the dolostone, which can be smaller than a pea or several feet across, and one cavity can hold anywhere from a few to a few thousand crystals. A useful tip is to break rocks that already show cavities on the outside. Some visitors find crystals simply by searching the rubble and quarry floor.
All land in New York belongs either to the government or to a private owner, and collecting on government land is illegal there, so stick to the fee mines or get permission.
"Herkimer diamonds" from elsewhere
Similar double-terminated quartz crystals are found in many other places, including Arizona, Afghanistan, Norway, Ukraine and China. They can look the same, but strictly only crystals from Herkimer County are Herkimer diamonds. In practice, double-terminated quartz is often labeled "Herkimer diamond" regardless of origin, so ask a seller where a crystal was found.
What is a Herkimer diamond traditionally associated with?
Herkimer diamonds are frequently used as talismans and amulets. In modern crystal traditions they are associated with clarity, attunement and dreams, and they are commonly linked with the crown chakra. Their double points lead some to describe them as stones that send and receive energy in both directions.
These are traditions and beliefs. They are part of why people choose Herkimer diamonds, not properties you can measure in the crystal.
Herkimer diamond jewelry
Herkimer diamonds are used to make natural crystal jewelry and are also faceted for jewelry and as collector gems. At 7 on the Mohs scale, they are durable for everyday wear.
How do you care for a Herkimer diamond?
- Wash it with warm water and mild soap, then dry it.
- Protect the points. Quartz has no cleavage but breaks with a shell-like (conchoidal) fracture, and sharp terminations can chip if knocked.
- Store it apart from harder gems, such as sapphire and diamond, which can scratch it.
How can you tell a real Herkimer diamond?
- Look for two natural points, one at each end, on a clear crystal with naturally glassy faces.
- Look for inclusions such as black hydrocarbon specks, common in genuine Herkimers.
- Ask where it was found. True Herkimer diamonds come from Herkimer County, New York.
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Frequently asked questions
Is a Herkimer diamond a real diamond?
No. It is a double-terminated quartz crystal. The name refers to its clarity and natural facets.
Where do Herkimer diamonds come from?
From cavities in dolomite in and around Herkimer County, New York, in the Mohawk River Valley. Similar crystals from elsewhere are often sold under the same name.
Can you dig for Herkimer diamonds yourself?
Yes. Fee-based mines near Middleville, New York, let visitors prospect and rent tools.
How old are Herkimer diamonds?
The host dolomite is about 500 million years old, from the Cambrian. The quartz crystals are thought to have formed later, in the Carboniferous Period.
What is a Herkimer diamond traditionally associated with?
In crystal traditions it is associated with clarity and dreams and linked with the crown chakra. These are traditional meanings rather than measurable properties.
How hard is a Herkimer diamond?
It rates 7 on the Mohs scale, like all quartz. Diamond rates 10.
Sources
- Wikipedia, Herkimer diamond: https://en.wikipedia.org/wiki/Herkimer_diamond
- Wikipedia, Cape May diamonds: https://en.wikipedia.org/wiki/Cape_May_diamonds
- Geology.com, "Herkimer Diamonds": https://geology.com/articles/herkimer-diamonds.shtml