  In an effort to better understand the role dark material plays in the
reflectance spectrum of carbonaceous asteroids, we performed laboratory studies
focusing on quantifying how the addition of relevant dark material (graphite,
magnetite and troilite) can alter the ultraviolet-visible and near-infrared
spectrum of a neutral silicate mineral. We find that addition of graphite,
magnetite and troilite all darken the reflectance spectrum of our forsterite
samples and cause the spectral slope to decrease (become blue). These spectral
changes can be caused by both nm- and micron-sized grains. In the
ultraviolet-visible region, we find that graphite is most efficient at altering
the spectral slope, while in the near-infrared, magnetite is the most
efficient. At all wavelengths studied, graphite is the most efficient at
darkening our sample spectrum. However, the observation that troilite also
alters the slope and albedo of our samples suggests that the spectral changes
caused by magnetite and graphite may not be unique. In addition, we find that
the spectral slopes in our mixtures compare generally well to what has been
observed on Bennu suggesting that a significant portion of fine-grained dark
material, including sulfides, present in the regolith can cause the observed
negative (blue) slope found on B-type asteroids.
