Fluorescent Minerals from the Permanent Collection On Permanent Display Lora Robins Gallery of Design from Nature, University of Richmond Museums On November 12, 2004, the Lora Robins Gallery of Design from Nature, University of Richmond Museums, opened the permanent exhibition Fluorescent Rocks from the Permanent Collection. Visitors to the exhibition will enter the display and see more than 350 visually unremarkable rocks. With a flip of a light switch, the specimens glow brilliant green, red, purple, and chartreuse. How does this happen and why? When certain minerals are exposed to different types of light (ultraviolet, infrared, x-ray, and even sunlight), electrons around their atoms absorb some of the energy. To return to the original state, these atoms eject this newly acquired energy as photons of light, which results in the unusual colors that are not visible in daylight.
This intriguing phenomenon is called fluorescence. The fluorescent minerals in this exhibition are exposed to both longwave and shortwave ultraviolet lights to bring out different colors from the same specimens. These minerals were donated to the museum in 1977 by Mrs. Lora McGlasson Robins, and in 1982 the Warner-Hunter Mineral Collection was donated by the Dulany Hunter Foundation and S. A. Dulany Hunter. The fluorescent rock display was co-curated by N. Elizabeth Schlatter, Assistant Director, University Museums, and Michael Reimer ('06), a biochemistry and studio art double major at the University of Richmond, and a 2004 University Museums’ Summer Research Fellow. How Do Minerals Fluoresce? Minerals are formed from the regular and repeated arrangement of atoms in a crystalline structure. Each atom is composed of a nucleus of protons and neutrons surrounded by a cloud of electrons. Exposure to ultraviolet light causes the electrons of a fluorescent mineral to become “excited” with energy. These excited electrons move into higher, less stable orbits around the atom’s nucleus. To regain stability, the electrons quickly return to their normal energy level and emit the excess energy in the form of photons of visible light (what we see as brilliant and unusual colors). It is often the presence of an impurity (called an activator) in a specimen that causes fluorescence. For example, red fluorescent calcite is activated by manganese present in only three percent of the sample. The History of Fluorescence Although the phenomenon of fluorescence has been observed for more than a thousand years, it was not until the 1850s that George Stokes, a professor of mathematics and physics at Cambridge University, coined the term “fluorescence” after the mineral fluorite, which sometimes glows blue in sunlight. By the 1930s, prospectors used portable ultraviolet lamps to identify minerals such as tungsten and uranium, which became essential to the military during and after World War II. Today, fluorescence has myriad practical applications in the fields of criminology and medicine, and it is used in the manufacturing of television screens and computer monitors. Fluorescent Minerals from the Franklin-Sterling Hill District, New Jersey Six cases in the exhibition are dedicated to minerals from the Franklin-Sterling Hill District in northern New Jersey. In this region alone, scientists have discovered at least eighty varieties of fluorescent minerals—more than any other site in the world. Quarries in this area contain unusual ore bodies of zinc, manganese, and iron. Many of the unique minerals found here are zinc derivatives of common minerals. For example, franklinite is a zinc enhanced version of magnetite, and it fluoresces in red and green. Willemite is a zinc silicate that fluoresces yellow-green.