Herkimer diamonds are not diamonds but unusually clear, doubly terminated quartz crystals that form in pockets in the Little Falls Dolomite of the Mohawk Valley. Visitors split and break the dolomite at fee mines around Middleville and St. Johnsville and keep what they find.
_(Herkimer_District,_New_York_State,_USA)_6.jpg){kind=link}
| Best places | Herkimer Diamond Mines (Middleville); Crystal Grove (St. Johnsville) |
|---|---|
| Cost | Fee per visit; some mines rent tools |
| Season | About April to October |
| Best time | After heavy rain, when crystals wash clean |
| What you will find | Clear, doubly terminated quartz crystals |
| What to bring | Rock hammer or small sledge, chisel, safety glasses, gloves, bucket |
| Closed | Ace of Diamonds |
Where to dig
- Herkimer Diamond Mines in Middleville: the largest and best known, with tools, a shop and a KOA campground. It opens in spring for the digging season.
- Crystal Grove Diamond Mine near St. Johnsville: digging plus camping.
- Ace of Diamonds, the neighbor of Herkimer Diamond Mines, is closed with no reopening announced.
What to bring
A rock hammer or small sledge, a chisel, safety glasses, gloves and a bucket. Some mines rent tools. Expect hot, exposed digging in summer and muddy pits after rain.
How to find them
- Search the loose rubble first; rain washes small crystals clean.
- Look for cavities (vugs) in the dolomite and split along them.
- Black hydrocarbon inclusions and skeletal crystals are prized.
When to go
The fee mines run from about April to October. After a heavy rain is the best time to surface-collect.
Fossils nearby
Penn Dixie Fossil Park near Buffalo is New York’s best public fossil site, with Devonian trilobites and brachiopods.
Questions
Where can you dig for Herkimer diamonds?
At fee mines in the Mohawk Valley, mainly Herkimer Diamond Mines in Middleville and Crystal Grove near St. Johnsville.
Are Herkimer diamonds real diamonds?
No. They are very clear, doubly terminated quartz crystals.
When are the Herkimer diamond mines open?
Roughly April to October; check the mine for exact opening dates.
Back to the New York rockhounding guide · Rules by land type