The reflectance of vitreous and metallic selenium has been measured in the spectral region between 550 and 1500 Å At the shorter wavelengths the metallic form is a very poor reflector, whereas the vitreous form has a reflectance comparable with that of glass.
WILLIAM L. GOFFE and M. PARKER GIVENS, "Reflectance of Vitreous and Metallic Selenium in the Vacuum Ultraviolet," J. Opt. Soc. Am. 53, 804-806 (1963)