Esperite is one of the 70 some fluorescent minerals from Franklin and Sterling Hill, New Jersey. It will fluoresce a nice yellow color under short-wave ultraviolet light. This fluorescent color is in striking contrast to the normal color of esperite. Under normal light, esperite is white or colorless. Fluorescence occurs when the ultraviolet light (invisible to humans) imparts energy to some of the atoms in the mineral. This energy is converted by the atom into visible light that we can then see. The following table shows the more common fluorescing minerals with their respective fluorescing colors, from Franklin and Sterling Hill, New Jersey.
These minerals are sometimes found in association with each other and can make for wonderfully colorful fluorescent specimens. Esperite is a product of the metamorphism of zinc minerals, such as hemimorphite and/or smithsonite, that were caught up in the regional metamorphism that created the wonderful Franklin site. Esperite is found in significant quantities only at Franklin and Sterling Hill, New Jersey.