As befits an educational institution, the Warren Museum does not merely have visually attractive displays of fluorescent materials; they are designed to be educational as well. Nearly all of the displays in the Warren Museum explore some theme of fluorescence, with the intent that the entire museum serve as a teaching aid during school tours, teacher workshops, and visits from university classes.
Our current themes include the following:
Individual Species Displays
Five large display cases in the Warren Museum each contain twenty or more specimens of a single mineral species. Each case thus has its own visual "personality" and illustrates the range in fluorescence of the same mineral from different localities.
Calcite case: The specimens in this case are all the same mineral—calcite—but they show a wide range in color of fluorescence, including red, green, blue, orange, yellow, white, and more. That a single mineral species can fluoresce in so many different colors highlights both the beauty and complexity of fluorescence in minerals. In viewing this case visitors will realize immediately that fluorescence cannot have a single cause.
Sphalerite case: The most common color of fluorescence in sphalerite is yellow to orange, but sphalerite can also fluoresce green, sky blue, greenish blue, lavender, reddish orange, pink, and white. Again the message is that different colors of fluorescence in the same mineral species must arise from different causes, a fact borne out by decades of laboratory experiments on synthetic sphalerite phosphors.
Scheelite case: As a counterpoint to the calcite and sphalerite cases, the scheelite specimens in this case, though originating from diverse localities worldwide, show little diversity in their color of fluorescence. Scheelite is a "self-activated" mineral-that is, its fluorescence is due to the mineral itself rather than to some chance chemical impurity or other cause. The characteristic blue to bluish-white fluorescence of this species is a valuable property in prospecting for scheelite deposits at night.
Fluorite case: Much fluorite fluoresces deep blue to blue-violet, but other colors of fluorescence are known, among them red, white to cream, and green. Red- and green-fluorescing fluorites are particularly rare but are represented among the specimens in this case. Fluorite is one of the most studied of all minerals, and the causes of its diverse colors of fluoresce are well known.
Willemite case: One of the principal ore minerals of the local zinc mines, willemite from Franklin and Sterling Hill is renowned for its exceedingly bright, yellowish-green fluorescence. Willemite from other localities, however, commonly fluoresces white to pale yellow, and rarely orange. Specimens from worldwide localities illustrate the range in color of fluorescence in this important mineral species.<
The various agents that cause minerals to fluoresce are collectively termed "activators". Here is where we illustrate some of the science of fluorescence, by showing a range of different activator types and revealing how dramatically they affect the fluorescence of the minerals that contain them.
Activators case: A label accompanying each specimen in this case identifies the cause of its fluorescence. Viewers learn that fluorescence commonly is due to inorganic chemical impurities, generally of metallic elements such as manganese, titanium, and the rare-earth metals, but occasionally of nonmetallic elements as well. Other minerals fluoresce due to included organic matter (microscopic droplets of petroleum in fluorite) or to nearly invisible coatings of a second mineral or alteration product.
Manganese-activated minerals: The fluorescence of every specimen in this display case is due to manganese. The colors of fluorescence span a broad range, from red through orange and yellow to green (but not blue!), showing that manganese causes different colors of fluorescence in different minerals. The colors are not accidental but depend on the atomic structure of the mineral in which the manganese is present.
Uranyl-activated minerals: The characteristic yellow-green fluorescence of uranyl-activated minerals is evident in all of the specimens in this case. Unlike manganese, the uranyl ion in minerals is quite insensitive to its atomic environment, and thus a similar color of fluorescence appears regardless of the mineral species.
It may seem obvious that different localities produce different fluorescent minerals, but just how different doesn't become apparent until suites of minerals from various areas are assembled and compared. None of the cases listed here resembles any of the others.
Northeastern U.S. case: Though mining has all but ceased in the northeastern United States, this region is still a prolific source of fine fluorescent mineral specimens. Most of the specimens in this case were collected during the 1990s or later, showing that some important localities are still productive. Others have been discovered only recently.
Fluorescent minerals of Arizona: Tens of thousands of abandoned mines in the deserts and mountains of Arizona provide fertile hunting grounds for collectors of fluorescent minerals, as the specimens in this case reveal. Recent advances in ultraviolet lamp technology have caused increasing numbers of collectors to take to the field in search of minerals for enjoyment, profit, and scientific research.
Ilímaussaq complex, Greenland: The Ilímaussaq igneous complex along Greenland's southwest coast furnishes some of the world's most lovely fluorescent minerals, including the iconic tugtupite, a mineral that fluoresces in a deep red color duplicated by few other mineral species. In this case you will not only see tugtupite from five different localities in the Ilímaussaq complex, but also fluorescent sodalite, analcime, polylithionite, and quartz. Almost nowhere else do igneous rocks look this good.
Horn Silver mine, Utah: Only two fluorescent minerals, sphalerite and calcite, are represented in this display, but their colors of fluorescence range from one end of the spectrum to the other. We can only guess at the activators - though this is an old locality, and now closed, its minerals have been little studied. To some of us the mystery only deepens the beauty.
Franklin and Sterling Hill, New Jersey: Our display of the local minerals is in Zobel Hall, not the Warren Museum, but we mention it here because it is so very different from the others. Fluorescent minerals from Franklin and Sterling Hill are the standard against which all others are measured. You’ll understand when you see them...
We've identified more than two dozen additional themes of fluorescence that one day we'd like to display. This will be a decades-long process, but listed below are a few miscellaneous themes on display now.
Fossils: Fossils often fluoresce in various pastel colors due to remaining traces of organic material, or they fluoresce green due to local concentrations of uranium-bearing minerals. The specimens in this case illustrate both of these general types and include fossil shells, coral, fish, bone, teeth, amber, and petrified wood. The presence of organic material in fossils tens to hundreds of millions of years old opens up exciting possibilities for biochemical research on organisms long extinct.
Terlingua-type calcites: The calcite specimens in this case are from widely separate localities on two continents, but they all share several properties: under shortwave ultraviolet light they fluoresce bright blue, followed by an enduring phosphorescence of the same color, but under longwave ultraviolet light they fluoresce pink to apricot to pale yellow, and phosphorescence is weak or absent. The probable causes are known but remain unproven.
Lapidary items: Numerous fluorescent spheres, eggs, carvings, cabochons, and obelisks are presented in this case, devoted to the lapidary side of the fluorescent-mineral hobby. Visitors wearing gemstones, such as diamond engagement rings or school rings, are invited to test them for fluorescence under the longwave ultraviolet lamps nearby.
Mineral crystals: One of our most generous patrons, George E. Hesselbacher, Jr. (1921-2001), specialized in fluorescent crystals (as opposed to the massive specimens that dominate most collections). Before his death George arranged for his finest crystal specimens to go on permanent public display in the Warren Museum, where they are now arranged in five "shadowbox" cases in the Hesselbacher Room.
Nonmineral items: Fluorescence is exhibited by a broad range of materials in addition to minerals. The items in this case include such materials as glass, ceramics, wood, paper, fabric, plastic, and paint. Common household objects remind visitors that one need not be interested in minerals to participate in the hobby of fluorescence.
Concrete: The multicolored fluorescence of sawn slabs of concrete from the ruins of mine buildings in nearby Franklin is a kind of accidental beauty. Workers in the late 1800s and early 1900s used fragments of dump rock from the mine as aggregate, and mill tailings for the sand, turning two waste products into free building materials. Most of this construction took place before the fluorescence of Franklin minerals was known.