Mercury's feldspar connection mid-IR measurements suggest plagioclase

Mid-infrared (7.5 - 13.5 mu m) spectra of Mercury at two equatorial longitudes obtained at the Infrared Telescope Facility (IRTF) at Mauna Kea Hawaii show spectral features indicative of plagioclase feldspar ((Ca,Na)(Al,Si)AlSi2O8)). Spectra resembling that of powdered labradorite (plagioclase: Ab(50)An(50) - Ab(30)An(70)) were obtained near similar to 120 degrees mercurian longitude. Spectra from a second region near similar to 30 degrees longitude resemble laboratory spectra from a lunar breccia made up of primarily plagioclase (probably anorthite, CaAl2Si2O8) and pyroxene fragments. Abundant feldspars of varying compositions on Mercury's surface indicate that the surface is heterogeneous and that the planet is highly differentiated. (C) 1997 COSPAR. Published by Elsevier Science Ltd.