This week, we will travel to one of the most mineralogically diverse areas, with the world’s largest assemblage of fluorescent minerals: The Sterling Hill-Franklin area of New Jersey. Bring your UV light!
Sharon Lyon
Editor, GeoLifestyle
Sterling Hill Mine, Ogdensburg, New Jersey
Ungvar/Shutterstock.com
The Sterling Hill Mine and nearby Franklin Mine are the world’s most famous zinc mines.
History:
The rich zinc ore was mined here beginning in the 1630s, and the area became the center for a large iron-making operation.
Major mining began in 1870, and in 1898, the New Jersey Zinc Plant in nearby Palmerton, PA, began production. The zinc was used to produce galvanized steel, tires, and brass. It was used by the military in both World Wars.
The deposits accounted for 15 percent of U.S. zinc production.
What you’ll see:
Principal ore minerals are willemite (zinc silicate), which fluoresces bright green under UV light, franklinite (iron-zinc-manganese oxide), and zincite (zinc oxide).
Calcite in the mine walls exhibits orange-red fluorescence.
Only at these mines: Their mines are renowned for the purity of the zinc ore, their variety of minerals, but especially for their spectacular fluorescent minerals. The area’s mines contain more fluorescent minerals than anywhere else in the world.
More than 360 minerals are known from the mines. Ninety-six of the minerals fluoresce, and 66 of these are not found anywhere else on earth.
Rare minerals first discovered here include hardystonite, esperite, clinohedrite, and johnbaumite.
Fluorescent minerals found in the Sterling Hill–Franklin area are listed here.
Geology of the area: The ore bodies are contained within the Precambrian (1.3-billion-year-old) Franklin Marble, which was deposited as limestone in an oceanic rift trough.
The ores likely originated as zinc-rich marine sediments, possibly similar to black-smoker sulfides. This unique genesis explains why the Franklin-Sterling Hill district is unlike any other geological setting worldwide.
During the Grenville Orogeny, 1 billion years ago, the rocks underwent extensive metamorphism.
Uplift and erosion exposed the ore bodies at the surface, and Pleistocene glaciers carried ore-bearing rocks to the south, creating placer deposits.
Trip tips: View the assortment of mining memorabilia, minerals, fossils, and meteorites in the Sterling Hill Mine Exhibit Hall.
Tour the Mine: There are 35 miles of tunnels in the Sterling Hill Mine, but most are inaccessible. The mine tour walks you through an upper section of the mine.
In the Rainbow Tunnel, you can see the walls glowing with fluorescence under short-wave UV lights.
The mine temperature is a constant 56° F, so bring a sweater.
Virtual option: If New Jersey is not on your travel schedule, tour the mine on YouTube.
Rockhounding at the mine: At Sterling Hill, you can collect minerals in two different sections of the Mine Run Dump—an international pile and a local pile. The local pile contains hundreds of tons of high-grade zinc ore from the mine, much of it fluorescent.
There is a shed with a shortwave UV light to check your rocks for fluorescence.
Bring your own bags or buckets. Hammers are not allowed.
Learn more about collecting minerals at the mine here.
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Zinciferous marble fluorescing at the Franklin Mine, New Jersey/Wikimedia Commons
The Franklin Mine, located 2.5 miles away from the Sterling Hill Mine, is equally famous for its remarkable fluorescent minerals.
What you’ll see: The mine stopped operating and closed to the public in 1954. Today, you can tour the museum and rockhound on the dump piles at the Franklin Mineral Museum.
View more than 10,000 mineral specimens in Baum and Welsh Halls, including local ore minerals.
The Fluorescent Room showcases hundreds of fluorescent minerals.
Step into the Mine Replica, housed in the original engine house, and used later as a training facility for miners.
Know before you go: The museum is open April–November.
Rockhounding at the mine: You can pay to see the museum and dig through the mine dump piles or skip right to the rocks.
Explore the world-famous Buckwheat Dump, a 3.5-acre field of rock known for its rare minerals.
Receive a collecting bag and can collect 2 pounds of rocks per person (extra fee for additional poundage).
A darkroom facility with UV lamps is available for viewing your specimens for fluorescence.
Extra fun:
The Franklin-Sterling Hill Gem and Mineral Show is 20–21 September at the Franklin Fire Department.
There will be a Night Dig on 4 October. Imagine the fluorescence in the dark!
Theme: This year’s theme is “Energy Resources for Our Future.”
This year’s theme will focus on the energy resources that shape our lives–from powering our homes to driving our industries.
For teachers: Educators can request an Earth Science Week Toolkit from the American Geosciences Institute.
The toolkit contains classroom activity pages, bookmarks, flyers, partners resource page, postcards, and posters. Highlights include the Earth Science Activity Calendar for the 2025–2026 School Year, and the poster-size geologic map of the United States.
There are also contests for students in photography, video, visual arts, and essay writing.
Order your toolkit today and mark your calendars for Earth Science Week!
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