Fluorescent Minerals: Spices of the Mineral World

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.

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.

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.

"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.