  Most brown dwarfs have atmospheres with temperatures cold enough to form
clouds. A variety of materials likely condense, including refractory metal
oxides and silicates; the precise compositions and crystal structures of
predicted cloud particles depend on the modeling framework used and have not
yet been empirically constrained. Spitzer has shown tentative evidence of the
silicate feature in L dwarf spectra and JWST can measure these features in many
L dwarfs. Here, we present new models to predict the signatures of the
strongest cloud absorption features. We investigate different cloud mineral
species and determine how particle size, mineralogy, and crystalline structure
change spectral features. We find that silicate and refractory clouds have a
strong cloud absorption feature for small particle sizes ($\leq$ 1 $\mu$m).
Model spectra are compared to five brown dwarfs that show evidence of the
silicate feature; models that include small particles in the upper layers of
the atmosphere produce a broad cloud mineral feature, and that better match the
observed spectra than the Ackerman & Marley (2001) cloud model. We simulate
observations with the MIRI instrument on JWST for a range of nearby, cloudy
brown dwarfs, demonstrating that these features could be readily detectable if
small particles are present. Furthermore, for photometrically variable brown
dwarfs, our predictions suggest that with JWST, by measuring spectroscopic
variability inside and outside a mineral feature, we can establish silicate (or
other) clouds as the cause of variability. Mid-infrared spectroscopy is a
promising tool to empirically constrain the complex cloud condensation sequence
in brown dwarf atmospheres.
