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Roger Weller, geology instructor

Quartz- Herkimer Diamonds
by Aislin Gonzales
Physical Geology
Fall 2014

Herkimer Diamonds

What are Herkimer Diamonds?

Herkimer diamonds is a generic name for a double- terminated quartz crystal discovered within exposed outcrops of dolostone in and around  Herkimer County, New York and the Mohawk River Valley.


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What do these diamonds look like?

These crystals have the typical hexagonal habit of quartz, (Shown above) However, instead of having a termination on one end they are doubly terminated. This is a result of the crystals growing with very little or no contact with their host rock. Terminated crystals that are double sided are very rare and this is part of what makes Herkimer Diamonds so popular with mineral collectors. They are brilliant, water clear quartz crystals composed with silicone dioxide, and hard enough to scratch glass.


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Where did Herkimer Diamonds originate?

The host rock for Herkimer Diamonds is the Cambrian-age, Little Falls Dolostone. The Little Falls Dolostone was deposited about 500 million years ago and the Herkimer Diamonds were created in cavities within the dolostone. These cavities are frequently lined with drusy quartz crystals and often are covered with a tarry hydrocarbon.  Dolomite limestone is the rock formation they are found in. Surface water containing silicon seeped downward through the cracks and was trapped in pockets or cavities in the dolomite rock.



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Who discovered the Herkimer Diamonds?

The Herkimer Diamonds of New York are not a recent discovery. The Mohawk Indians and early settlers knew about the crystals. They found them in stream sediments and plowed fields. These people were amazed and awed with the crystals and immediately held them in high esteem.  Because the Mohawk Indians discovered them they were known as “The People of the Crystals”.

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The Herkimer Diamond mines:

Some of the best places to find Herkimer Diamonds today are located along New York State Route 28 in Middleville, New York. When visiting this area it is important to remember that all land in New York either belongs to the government or is private property. Collecting minerals from government lands is illegal in New York and collecting on private property always requires permission in advance.
The two commercial mines are the
Ace of Diamonds Mine, and Herkimer Diamond Mine. Both allow collectors to enter and prospect for a nominal fee. Both locations also rent equipment such as hammers, wedges and other small tools. They also have small exhibit areas where you can view or purchase specimens.


How do you find Herkimer Diamonds?

 “Find and Break Prospect” The easy way to prospect is to find pieces of vuggy rock and break them open with a heavy hammer. If you are lucky the rock will break to uncover one or several Herkimer Diamonds within a cavity. If your visit to the mine will last just a few hours or even a single day this is a good way to spend your time. Dolomite is a very tough rock so expect to work hard. The use of safety glasses is required and wise collectors wear gloves to protect their hands. They always wear jeans or heavy long pants and a long sleeve shirt for "find and break" prospecting. Small pieces of dolomite will sometimes fly when a rock breaks and they can easily cut or bruise a person wearing short pants. The "find and break" prospecting method described above is engaged by many people who visit these mines and can lead to a few good finds. The keys to success are selection of good rocks to break and do not be discouraged if you break fifty rocks without finding a crystal.


Scavenger Prospecting

Some visitors to the mines have been successful by simply searching the rock rubble for exposed crystals or searching the quarry floor for crystals that may have dropped while being mined. People have found several really nice crystals this way and lots of tiny ones. People have also seen children find many nice crystals this way.


“Cavity” Prospecting

For finding large quantities of crystals, the most successful mining method is to break into large cavities in the quarry walls and floors using sledge hammers and wedges. This method requires tools, patience, time and knowledge of how to break an extremely durable dolostone. Power equipment is never allowed in the mines.


Lucky You

If a collector is lucky and determined to prevail over the durable dolostone, the reward could be breaking into a cavity. These cavities can contain a few to a few thousand nice Herkimer Diamonds that range in size from a couple of millimeters to over twenty centimeters in size. Perfect single crystals, doubles and crystal clusters might all be found in a single cavity.



Fake Diamonds Are a Girl’s Best Friend

Why hunt for Herkimer Diamonds? It's great fun and every time you break open a rock you will look with anticipation to see if you liberated an unseen quartz crystal. Nice Herkimer Diamonds are highly prized mineral specimens and are sought by mineral collectors worldwide. Large numbers of Herkimer crystals are also used in jewelry because their natural facets are both beautiful and interesting. Some people also seek Herkimer diamonds because they are thought to have "holistic qualities". If you like minerals and have an opportinity to visit the Herkimer County area of New York, consider spending a day looking for Herkimer Diamonds. Be sure to wear clothes that are suitable for working outdoors. Safety glasses are required and you will be sorry if you don't wear gloves. If you need a sledge hammer or other tools you can rent them at the mine for a very small fee.


Geology Sources:



To purchase some: