Gerstmannite under longwave UV Light

Under conventional (mercury-vapor) LW ultraviolet light, the gerstmannite in this specimen (same one as in photos GST3a and GST3b) shows only a dim, barely perceptible, gray to tannish-gray response while the underlying sphalerite fluoresce bright orange.  The tiny, blue-fluorescing grains along the gerstmannite-sphalerite contact are sphalerite as well.  The blue response is a common one in Sterling mine sphalerite and is strongly activated by UV light in the 300 to 330 nm wavelength region but falls off rapidly at higher wavelengths (E.R. Verbeek, unpub. data, 2011).

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