Tucked into the hills of Sussex County, the borough of Franklin, New Jersey holds an official title you won’t find anywhere else on Earth: the Fluorescent Mineral Capital of the World. Flip off the lights inside an old zinc mine here, switch on an ultraviolet lamp, and plain gray rock erupts into neon streaks of orange, green, and red. It’s not a gimmick or a light show someone rigged up for tourists — it’s real geology, and it only happens quite like this in one small corner of New Jersey.
Why Is Franklin, NJ Called the Fluorescent Mineral Capital of the World?
The nickname isn’t just local bragging rights. On September 13, 1968, the State of New Jersey passed a resolution declaring the Borough of Franklin “the Fluorescent Mineral Capital of the World.” The title exists because of what’s sitting underground: Franklin is located over a rich ore body containing more than 150 minerals, many of them fluorescent and 25 of which are found nowhere else on earth.
Zoom out to the whole mining district, which includes neighboring Ogdensburg, and the numbers get even wilder. The Franklin-Sterling Hill mining district of New Jersey is geologically unique with over 360 minerals found in one locality, 8% of all known minerals and more than anywhere else in the world; over 85 of the minerals found here fluoresce, which is also a world record. No other single spot on the planet packs in that much mineral diversity, let alone that much glow.
The Science Behind the Glow
Fluorescence happens when certain minerals absorb ultraviolet light and re-emit it as visible color. Under a black light, the effect at Franklin and Sterling Hill is dramatic. Formerly pale, flat, unlit rocks and minerals turn vibrant orange, pink, and green when the overhead lights are turned out and the black-light turned on, streaking with red or developing otherworldly glowing veins of light that weren’t visible before. Two of the star minerals responsible are calcite and willemite — and interestingly, most of the orange is calcite and the green is willemite, even though under white light, calcite is usually white to gray, and willemite is red or green. Same rock, completely different personality depending on the light you shine on it.
Where to See the Glowing Rocks in Person
You’ve got two main stops, both within a short drive of each other, and honestly, mineral nerds tend to do both in a single day.
Sterling Hill Mining Museum’s Rainbow Tunnel
In Ogdensburg, the Sterling Hill Mining Museum lets you walk into an actual former mine. You can take a quarter-mile underground walking educational adventure into the fourth oldest mine in the country and the last working underground mine in NJ. The highlight is the appropriately named Rainbow Tunnel — along the way you’ll see a mining equipment history display, a drilling and blasting demonstration, and the world-famous fluorescent “Rainbow Tunnel,” where everybody gets to take home a fluorescent mineral specimen.
The mine itself once ran remarkably deep. At one point, the mine reached 2,675 feet below the surface with 35 miles of tunnels, but now only the upper level remains since everything below it flooded. Today it’s recognized well beyond just local pride — the mine was placed on both the New Jersey Register of Historic Places and the National Register of Historic Places in 1991. The whole operation grew out of the mine’s closure: the museum was started by brothers Richard and Robert Hauck in 1990 in the shuttered Sterling Hill zinc mine, which had closed three years earlier, and in 1999 the museum created a special wing known as the Thomas S. Warren Museum of Fluorescence, named in honor of Thomas S. Warren, an ultraviolet researcher and designer of the mineralight portable black-light lamp, to house the growing glow-in-the-dark collection.
Down in the tunnels, expect it cool and a little damp — the air inside the mine is cool and damp, always around 56°F, so you may want a sweater. Bring a light jacket even in July.
Franklin Mineral Museum and the Buckwheat Dump
A few miles away in Franklin proper sits the Franklin Mineral Museum, which pairs display cases of labeled specimens with a hands-on outdoor mine dump. The museum signage tells visitors that 357 different mineral species were found in the zinc deposits, and there are long glass display cases of rocks that have been identified and meticulously labeled. Out back is the famous Buckwheat Dump, where thousands of rockhounds still clamber over the heaps looking for glowing nuggets decades after the mines went quiet.
Can You Actually Dig Your Own Fluorescent Rocks?
Yes — and that’s arguably the best part. At Sterling Hill, you can collect minerals from all over the world, including fluorescent ones, yourself any day the museum is open, and the museum also runs a Rock Discovery Center, Fossil Discovery Center, sluicing, mineral collecting, and an astronomical observatory. Over at Franklin Mineral Museum, visitors can purchase admission to just the museum, just access to the mine dump — which includes keeping two pounds of the mineral specimens you collect — or a combination ticket for both at a discount.
If you want to go beyond a casual scoop-and-look, serious collectors show up with real equipment. Recommended gear includes sturdy boots, UV protection safety glasses, a geologist’s hammer, a chisel, a backpack or bucket, a heavy dark cloth or black tarp, and a shortwave and/or longwave ultraviolet lamp. Some events even happen after dark — the museum offers periodic mineral collecting on the property where you can find some of the rarest fluorescent minerals on earth, including night collecting with a hand-held fluorescent lamp you bring yourself.
Planning Your Visit
Tour length matters here, so don’t plan this as a quick pit stop. The museum offers public tours daily from April through October and on weekends in November and December, and each tour takes at least two hours. Walking underground is easy on the legs, at least — it’s all level walking inside the mine. Hours can shift seasonally, so it’s worth checking ahead; as one visitor guide notes, the public tour operating schedule changes with the seasons.
Both sites are easy to reach if you’re driving up from the New York metro area. Signs make both sites quite easy to find while driving north on NJ Route 23.
Why This Odd Corner of New Jersey Is Worth the Drive
There’s something genuinely disorienting about standing in a pitch-black tunnel and watching ordinary rock turn into something that looks lifted from a science-fiction set. This isn’t a painted attraction or a projection trick — it’s leftover ore from a working mine that shut down decades ago, glowing because of chemistry that took roughly a billion years to set up in the first place, per geologists who’ve studied the deposit. If you’ve already done the boardwalks, the lighthouses, and the roadside oddities New Jersey is famous for, Franklin and Ogdensburg offer something stranger and quieter: an entire town built on rocks that only reveal their real colors once you turn the lights off.
NOTE TO THE ADVENTURER: This guide is meant to spark curiosity for what lies beyond the horizon — not to serve as a guarantee. Roads fall into disrepair, buildings are torn down and rebuilt, and properties change hands; 'tis your responsibility to do your own research before setting out. Always heed local and regional law, and always respect ground that isn't your own. Take every entry here as a suggestion, not a decree. This guide's contents were gathered with the aid of artificial intelligence, and like any scout, it will from time to time lead you astray. You assume all risk in following its counsel, and neither this blog nor its author is liable for any loss, injury, or misfortune that results.
