Herkimer Diamond Mines

A doubly terminated quartz crystal, naturally faceted on both ends, found in vugs in the Cambrian dolomite of the Mohawk Valley in New York. It is quartz, not diamond. The nickname comes from the crystals' unusual clarity and well-formed faces, and local names Middleville diamond and Little Falls diamond record the earliest discovery sites.

No. Daily wristbands are purchased on site at Miners' Village, and the mines run 9 a.m. to 5 p.m. daily in season, rain or shine. Status varies between the individual quarries in the area, though, so confirm which are open before travelling: the Ace of Diamonds Mine in Middleville has been reported closed for the 2026 season.

A 3 to 4 pound crack hammer or small sledge, cold chisels, safety glasses, heavy gloves, knee protection and a bucket. Egg cartons or bubble wrap protect crystals on the drive home. Beginners often do just as well picking over broken spoil piles, where crystals loosened by earlier diggers turn up with no hammer work at all.

In two stages. The host dolomite was deposited in a shallow sea about 500 million years ago in the Cambrian. Much later, acidic water dissolved small cavities called vugs in the buried rock, and during the Carboniferous quartz crystallized inside them very slowly, which produced the exceptional clarity and the terminations on both ends.

Yes. The Herkimer Diamond KOA Resort occupies the same property at 4626 State Route 28 North, operating roughly April 11 through October 31, and the mines are open daily during the season. That makes it practical to dig over two days without relocating.

Not reliably. The valley's productive ground is in commercial fee-dig quarries on private property, and collecting from road cuts or private outcrops without permission is trespass. The fee mines are the legitimate route, and a daily wristband at the Herkimer operation covers a full day of digging.

Look for vugs, small cavities in the dolomite where the crystals grew. Experienced diggers work a hard face with hammer and chisel, listening for the hollow sound that signals a cavity, and follow seams. Beginners often do better picking over broken spoil piles, where earlier diggers have already loosened crystals.

As specimens rather than as gems. They are quartz, not diamond, so the value is in clarity, crystal form, size and inclusions rather than in any gemstone rarity. Exceptional large clear doubly terminated crystals and pieces with striking hydrocarbon or fluid inclusions command the most among collectors.

Usually hydrocarbons, a solid black bitumen-like material trapped as the quartz grew. Crystals also contain saltwater or petroleum liquid, carbon dioxide gas and negative crystals, all of which record the conditions inside the vugs during the Carboniferous when the quartz crystallised.

It has been reported closed for the 2026 season, and neighbouring operations in the Mohawk Valley have opened and closed year to year. Confirm which quarries are running before you travel. The Herkimer Diamond Mines operation attached to the KOA resort is the most consistently open of the group.

Both approaches have their advocates and the honest answer is that they suit different visitors. Working a hard dolomite face with hammer and chisel is where the large clean pockets come from, and people who commit to one face for hours report the best finds. Picking over broken spoil requires no strength or technique and reliably produces small crystals, which is why it is so often recommended for children and first-timers. Most experienced diggers describe doing both across a day.

A three to four pound crack hammer rather than a full sledge comes up most, paired with several cold chisels of different widths, because chisel work into seams opens vugs that brute force would shatter. Safety glasses are described as non-negotiable by everyone, along with heavy gloves and knee protection. Several people also recommend egg cartons or bubble wrap for the drive home, since the crystals chip against each other in a bucket.