  We present a compositional analysis of the 10 micron silicate spectra for
brown dwarf disks in the Taurus and Upper Scorpius (UppSco) star-forming
regions, using archival Spitzer/IRS observations. A variety in the silicate
features is observed, ranging from a narrow profile with a peak at 9.8 micron,
to nearly flat, low-contrast features. For most objects, we find nearly equal
fractions for the large-grain and crystalline mass fractions, indicating both
processes to be active in these disks. The median crystalline mass fraction for
the Taurus brown dwarfs is found to be 20%, a factor of ~2 higher than the
median reported for the higher mass stars in Taurus. The large-grain mass
fractions are found to increase with an increasing strength in the X-ray
emission, while the opposite trend is observed for the crystalline mass
fractions. A small 5% of the Taurus brown dwarfs are still found to be
dominated by pristine ISM-like dust, with an amorphous sub-micron grain mass
fraction of ~87%. For 15% of the objects, we find a negligible large-grain mass
fraction, but a >60% small amorphous silicate fraction. These may be the cases
where substantial grain growth and dust sedimentation has occurred in the
disks, resulting in a high fraction of amorphous sub-micron grains in the disk
surface. Among the UppSco brown dwarfs, only usd161939 has a S/N high enough to
properly model its silicate spectrum. We find a 74% small amorphous grain and a
~26% crystalline mass fraction for this object.
