Fluorescent Minerals: Spices of the Mineral World

Brooklyn Children's Museum

The geology collection at Brooklyn Children’s Museum features more than 7,000 rocks and minerals from around the world. This exhibit highlights specimens that look rather dull at first glance. But travel back in time and examine them through the eyes of the Museum’s mineral club of the 1930s. Through the club's adventures, we discover that these minerals have secrets up their sleeves—they’re fluorescent. View them in a different light to see them transform from ho-hum to magnificent.

Our story begins with fluorite. "Fluorite" sounds a lot like “fluorescent.” That’s because the phenomenon of fluorescence is named after this mineral.

This specimen from Alston, England shows exactly why.

When ultraviolet (UV) light shines on it in a dim room, it becomes a glowing blue-violet nugget.

This magnificent color shift in response to UV light is fluorescence.

This fluorite from Clay Center, Ohio shows a different response to UV light.

In fact, fluorite is famous for fluorescing the greatest variety of colors. But a lot of fluorite doesn't fluoresce at all.

So, fluorite gives us a good idea of the surprises that await in the fluorescent mineral world.

For the rest of our fluorescent mineral story, we travel back in time to the Brooklyn Pick and Hammer Club. Mr. Boyle, the Museum’s mineralogist, started the club in 1934.

The club “had especially good times investigating the mineral world,” said Mr. Boyle. We relive their good times by thumbing through The Children's Museum News, a monthly newsletter Museum staff wrote.

The club also told all about their adventures in Pay Dirt. The kids printed this newsletter on an old-timey printing press in the Museum's basement.

Pictured: Mr. Boyle, wearing a hat at far right, shows the club how to examine rocky outcrops in Central Park near 59th Street. It's Manhattan schist, they discover. When schist is near the ground surface, it signals a strong foundation for building skyscrapers.

Some of the club’s best times were on field trips. On trips, Mr. Boyle showed them where to collect minerals and how to investigate rocks that form the city.

“There are a number of places in Greater New York where the rock strata are… being blasted away for the construction of roads, subways, [and] buildings…

The rocks are being dumped in...Riverside Drive, Flushing and elsewhere. Inwood Park, the Harlem River Speedway, the Bronx River valley, the Palisades, and Staten Island are a few more places where minerals may be found.” —Abraham Spector, Pay Dirt, June 15, 1938

Pictured: Alan Bergdahl (seated), D. Luchter, Alexander Nicolescu, and Carmine Venuto (hammering) collecting garnets in schist along the Harlem River near 170th St.

“When we reached the outcrops above the speedway, at 170th street, we examined the Manhattan schist… We saw a few garnet-studded schist outcrops…which had been transported by the glacier from the Palisades…

We closed the day at a rock dump near the Hendrik Hudson Bridge, where we collected some good brown tourmaline and pyrite crystals.” —Irving Horowitz, Pay Dirt, May 15, 1940


Back at the ranch, the club investigated their cargo in the Museum’s mineral lab.

“The mineral laboratory! That was hallowed ground…A new world…opened to me. I saw crystals whose beauty and delicacy could not be surpassed by man’s genius.” —Alexander Nicolescu, undated Pay Dirt issue, about 1938

Pictured, clockwise from left: Irving Horowitz, Herbert Rosenblum, and Leon Dressner tinker with lab tools and specimens from the Museum's collection. The club shows off recent field trip finds in the case at lower right.

Fluorescence was a topic that had “long spiced" the club's activities.

Irving Horowitz tells all about fluorescence in this article, read from right to left. He highlights discoveries scientists made by accident. These experiments enabled the world to enjoy fluorescent minerals.

We also learn that many club members won prizes outside the Museum for sharing fluorescent mineral discoveries.

Our friend Irving mentioned that “some of the members have constructed iron arcs which are very rich in ultraviolet light.”

An iron arc was a gadget used to see minerals fluoresce back in the club's day. Today's convenient UV lamps were unavailable. The club also used argon bulbs, which were cheaper than iron arcs, but also weaker. They produced a less impressive fluorescent mineral show.

Pictured: Kids who couldn't afford an iron arc must've appreciated Seymour Scharf's tutorial on how to build one. He calls it an iron spark gap in "A Fluorescent Lamp."

This chart shows which minerals the club was investigating and three light sources they used to see them fluoresce. Each source produced UV light in different amounts and at different wavelengths, called shortwave and longwave. Under each light, the same specimen might fluoresce a different color or not at all.

We used this chart to select—and to rediscover—the fluorescent minerals featured in this exhibit. Since the club's day, affordable, consistent, easy-to-use UV lights were invented. In this exhibit, the minerals are fluorescing under a longwave UV lamp.

How Fluorescence Works
“Fluorescence is the emission of light of one color when light of a different color (wavelength) falls upon certain substances. Usually, however, light which causes fluorescence does not have any apparent color because that kind of light, which may be ultra-violet or x-rays, is invisible to the human eye. " —Irving Horowitz, Pay Dirt, Nov. 1, 1940                                                                                                                                                                 Pictured: Hackmanite from Bancroft, Ontario, Canada in white light.

When we shine UV light on this hackmanite, it absorbs a little. That extra energy excites electrons in the mineral’s atoms.

To get back to "normal," the electrons release some energy as light we can see—in this case, mostly orange light.

More than UV light is required to excite fluorescence. Actually, when we consider all known minerals, few fluoresce.

The club knew about many fluorescent minerals, but we don’t know if they knew what causes fluorescence. In the club’s day, scientists were still trying to answer this question.

Pictured: Sodalite from Bancroft, Ontario, Canada in white light.

Today we know that fluorescence is often accidental. For example, traces of impurities, called activators, activate fluorescence in many minerals. In fact, purer minerals don't usually fluoresce.

Sulfide impurities activate fluorescence in some sodalite specimens. This one's from Bancroft, Ontario, Canada. The area is famous for spectacular fluorescent sodalite.

Manganese impurities activate fluorescence in willemite from Franklin, New Jersey.

Franklin is called "the fluorescent mineral capital of the world." Its mines yielded more fluorescent minerals than any other locality.

For many fluorescent mineral collectors, Franklin willemite is the best example of a fluorescent mineral.


This rock is also from the Franklin, New Jersey mining area. It's a mix of willemite and another fluorescent mineral—calcite.

Manganese is the impurity activator in this rock, too. But it activates purplish pink fluorescence in calcite, and green in willemite. The black areas are franklinite, which doesn't fluoresce.

Franklin is famous for these striking combinations. The mines closed in the 1950s. Originally mined for zinc, the minerals were all used up.

Although manganese impurities activate fluorescence in calcites from Franklin, NJ, it's not the activator in all fluorescent calcites.

Unique conditions of the earth produce unique fluorescence in Terlingua, Texas calcites. Scientists are still uncertain about its activators.

Fluorescence is self-activated in a few minerals. For example, fluorescence is a natural property of autunite itself, not a result of impurities.

So, autunite fluoresces consistently no matter where it's from.

Autunite contains the element uranium. Thanks to uranium's uranyl ions, autunite consistently fluoresces bright yellow-green.

The consistent fluorescence of autunite and other uranium bearing minerals helps miners find them.

More so in the past than today, people mined uranium bearing minerals to make a pigment. It was used to color glassware yellow-green.

Glassware colored with uranium retains the fluorescence of the mineral source.

Fluorescence was unintentional in the design of older objects like this candy dish from about 1875. Today, many people collect uranium glass just to see it fluoresce.

Sometimes museums discover "new" things made with uranium glass in their collections. It was a surprise to learn that uranium glass was used for dolls' eyes.

Pictured: Effanbee Candy Kid doll made in New Jersey about 1946-1950.

Are this doll's fluorescent eyes uranium glass? The Museum is still researching this question, but it looks like it!

Pictured: Effanbee Candy Kid doll made in New Jersey about 1946-1950.

The beauty of fluorescent minerals inspired the Brooklyn Pick & Hammer Club to investigate them. But the club was also interested in using them to help people.

Wernerite from Grenville, Quebec, Canada was the subject of one experiment.

The club considered wernerite the most fluorescent mineral.

Alan Bergdal used wernerite to test a DIY sunscreen recipe in "Vinegar, Sunburn and Fluorescence," Pay Dirt, August 1, 1938.

Sphalerite is a reminder that as much as we know about fluorescent minerals, our understanding is still rocky.

Scientists can replicate some mineral fluorescence in labs, but the fluorescence of sphalerite from Frisco, Utah is something we can only see in nature.


Pictured: Mr. Boyle on a jetty in Breezy Point, Queens, New York.

Jack Claudius Boyle, the Museum’s first mineral curator, knew that fluorescing is one of the most spectacular things rocks do. In 1928, he helped mount the first fluorescent mineral museum exhibit in the United States at the Academy of Natural Sciences in Philadelphia. The next year, he was at Brooklyn Children’s Museum using fluorescence to spark kids’ curiosity about Earth.

During his time with the Museum (1929-1947), Mr. Boyle pioneered a hands-on, investigations-based approach that made it fun for kids to learn about science. He inspired countless boys and girls to embark on lifelong journeys in science, technology, engineering, and math.

“Miriam P. Sachs, who has been working under Mr. Boyle’s direction at the Children's Museum for some time,…entered the University of Minnesota because she decided that it offered the best college course in geology. She is the only girl taking the course.”

"Jane Kessler, another Children’s Museum girl who specialized in mineralogy, is in the midst of her second year teaching geology at Virginia Polytechnic Institute.”
—Children’s Museum News, March 1937

Later, Jane bought Mr. Boyle's personal mineral collection. She donated it and her own collection to Virginia Polytechnic Institute's Museum of Geosciences. They're still used for education and exhibits. Jane was likely one of America's first formal female geologists.

"...David studied minerals in the Museum laboratory and for years he talked about becoming a mining engineer. He graduated from high school full of hopes and dreams only to be told that his family had no money to help him on his career.

David…sold his mineral collection, built up over years of Museum field trips and excursions on his own, and received enough to take him to the Colorado School of Mines.”

Children’s Museum News, Oct.-Nov. 1940

Pictured: Edward Fairstein rolls out the latest issue of Pay Dirt on a printing press in the Museum's basement.

In mineral club, Edward Fairstein met lifelong friend Elliot Juni, who convinced him to go to college. Ed became an award winning nuclear engineer. He invented nuclear measurement instruments and consulted for NASA. Mr. Boyle had introduced Ed to uranium minerals, the source of nuclear energy.

Ed and other club members stayed in touch. Over the years, they shared memories of how Mr. Boyle had sparked their interest in science.

Pictured: Carl Supp, 20, works gems in his basement to make some cash while in college. He learned how to construct the machines and polish minerals at the Museum.

"As we go to press, we learn that Carl Supp has been appointed to a position in the Baltimore, Md. Office of the U.S. Coast and Geodetic Survey. Carl first came to the museum in the early 1930s, and his interest in minerals lead him into the work of cutting and polishing gem materials.”—Pay Dirt, April 15, 1940

Carl became an engineering geologist. He helped build the Chesapeake Bay Bridge and highways.


Pictured: Irving Horowitz, lower left, works on a map in the mineral lab.

At the U.S. Coast and Geodetic Survey, Carl Supp bumped into Irving Horowitz. At the Survey, Irving was a junior draftsman. He helped make aeronautical charts and maps for the Allied forces during World War II. His mapping and charting skills stemmed from mineral club.

After the war, he taught earth science for almost 50 years in New York City public schools and at Brooklyn College. He rewrote the textbook students used to prepare for the New York earth science regents exams. He drew inspiration from activities he'd enjoyed in mineral club. Irving dedicated Earth Science Investigations to the memory of Mr. Boyle.

"I used to get to the Museum on ball bearing roller skates," Irving Horowitz recalls. Now 93, he still finds endless enjoyment in his own mineral collection. Irving even kept specimens from Mr. Boyle. He shares the story with his children and grandchildren.

Pictured: Irving Horowitz shows his fluorescent tugtupite specimen from Greenland glowing under a shortwave UV lamp.

Irving's favorite mineral "spice" is one the club would not have known—tugtupite. The rare mineral wasn’t identified officially until about 1960.

Credits: Story

Sandra Vanderwarf, Curator
Sophia Figuereo, Curatorial Assistant
Erik Fiks, Photography
Roberto Portillo, Photography


Special thanks to Irving Horowitz, Samuel Bristow Photography, and The Fluorescent Mineral Society for sharing generously their expertise.

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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