Why rockhounds from across the country keep making the drive to Franklin, New Jersey

Franklin’s rocks glow in the dark

About an hour from New York City, tucked into Sussex County at the edge of the Appalachians, Franklin sits on one of the most mineral-rich patches of ground on the planet. The rocks here don’t just look unusual.

Under ultraviolet light, they explode into colors. This isn’t a special exhibit or a trick of the light.

It’s the geology. And you can take a piece of it home.

From iron furnace to zinc mining boomtown

Franklin started as a village called Franklin Furnace in the 1600s, where early settlers smelted iron along the Wallkill River. Zinc changed everything.

By the early 1800s, commercial mining had begun, and by 1897, a string of small companies merged into the New Jersey Zinc Company. Workers came from Russia, England, Hungary and Poland to fill the mines.

The town officially became the Borough of Franklin in the early 1900s, built almost entirely around what was underground.

More than 350 minerals and 19 found nowhere else on Earth

Scientists have confirmed more than 350 different mineral species in the Franklin area. About 19 of them exist nowhere else on the planet.

The ore body also holds franklinite, willemite and zincite, the three minerals that drove a century of zinc mining.

Researchers rank this area among the most complex mineral sites in the world, not just in the United States.

That density of rare minerals in a single location is what makes the geology here so different from anywhere else.

Franklinite was named after Benjamin Franklin himself

In 1819, French geologist Pierre Berthier first described a black, shiny mineral with sharp crystal formations pulled from these mines. He named it franklinite in honor of Benjamin Franklin.

For more than a century, it served as New Jersey’s main source of zinc. The state didn’t let that history fade.

In 2023, New Jersey made franklinite its official state mineral, more than 200 years after Berthier first put a name to it.

How Franklin got its official glowing rocks title

On Sept. 13, 1968, New Jersey passed a resolution declaring Franklin the Fluorescent Mineral Capital of the World. The title recognized something no other place could match.

More than 90 different minerals in the area fluoresce under ultraviolet light, and no other town in the country carries that distinction. The resolution made official what rockhounds and geologists had known for decades.

The rocks under Franklin do something the rocks under everywhere else simply don’t.

Step into the darkroom and watch the walls come alive

The Franklin Mineral Museum opened in 1964, founded by the Franklin Kiwanis Club.

Inside, a darkroom lets you stand in front of rock specimens and watch them shift from dull gray to vivid pinks, greens and oranges the moment the ultraviolet lamps come on.

The museum also holds exhibits on fossils, petrified wood and Native American artifacts, plus a mine replica that shows what the underground work actually looked like.

It’s one of the best public displays of fluorescent minerals anywhere.

A 32-foot wall of glowing rock lights up the main hall

Welsh Hall holds more than 5,000 specimens from around the world. The Local Minerals Room shows off species found only in Franklin.

Walk into the Fossil Room and you’ll find dinosaur eggs, shells and petrified wood. A 32-foot wall of fluorescent rocks runs along one side, and when the room goes dark, it lights up in layers of color.

A separate room holds stone tools made by the Lenni Lenape people who lived on this land long before the mining began.

Dig the Buckwheat Dump and keep what you find

Behind the museum sits a three-acre pile of mine waste rock called the Buckwheat Dump, named after a farm field that once stood there. The pile is open to visitors whenever the museum is.

Bring gloves and dig. Collectors have pulled specimens worth hundreds of dollars from the same ground everyone else walks past. Whatever you find goes home with you.

The site has been open to rockhounds for decades, and there’s still plenty left to discover.

Willemite, calcite and four colors in a single rock

Not all the colors are the same. Willemite glows bright apple green under ultraviolet light.

Calcite from Franklin glows deep red. Hardystonite shines purple-blue, and clinohedrite gives off a soft orange.

Some single rocks contain four or more colors layered into one piece. The effect isn’t from paint or treatment.

It comes straight from the mineral chemistry locked inside the rock. That’s why the darkroom displays hit so differently here than at any other museum.

Go underground at Sterling Hill Mine

Three miles away in Ogdensburg, the Sterling Hill Mine takes you into the real thing. Guides hand out hard hats before you walk into tunnels the miners actually worked.

The mine reached 2,675 feet below the surface at its deepest point. Many of the guides are former miners, and they don’t read from scripts.

They talk about working these tunnels from memory.

Life-size mining displays line the route, but the guides’ stories are what stay with you after you come back up.

The Rainbow Tunnel turns the mine walls into a light show

Deep inside Sterling Hill, there’s a section called the Rainbow Tunnel where the walls run thick with glowing ore. The guide cuts the lights and switches on ultraviolet lamps.

Reds, greens and yellows break across the rock in every direction. There’s no paint, no projection, no setup.

The color comes from the minerals in the walls, the same minerals that drew miners and scientists here for over a hundred years. First-time visitors tend to go quiet the moment it happens.

The old mine replica inside a historic engine house

Back at the museum, the mine replica sits inside the former Taylor mine engine house, listed on the New Jersey State Historic Site Register. The New Jersey Zinc Company originally built it as a training space.

Now it lets you see what underground mining looked like without going below ground. Old candle hats, air pressure drills and other tools line the displays.

The inside stays cool, the way a working mine does, and the layout gives you a clear picture of what the men who dug this town out of the earth actually dealt with every day.

Visit the Franklin Mineral Museum in Franklin, New Jersey

You can dig the Buckwheat Dump and walk the museum exhibits all in one visit.

The Franklin Mineral Museum at 32 Evans St. opens seasonally from early April through late November. Admission covers both the museum and dump access.

A gift shop sells ultraviolet lights if you want to check your finds on the spot.

Call ahead or check the official website for current hours and pricing before you go, since seasonal schedules can shift.

This article was created with AI assistance and human editing.

Read more from this brand:

• New Jersey’s 90-ton elephant has stood on the beach since 1881 — and you can climb inside her
• The little-known German bombing in NY that pulled the US into WWI
• U.S. Marines hated these early Colt revolvers, but the Texas Rangers loved them – here’s the story