  We report spectra obtained with the Spitzer Space Telescope in the wavelength
range between 14 microns and 35 microns of 19 nearby main-sequence stars with
infrared excesses. The six stars with strong dust emission show no recognizable
spectral features, suggesting that the bulk of the emitting particles have
diameters larger than 10 microns. If the observed dust results from collisional
grinding of larger solids, we infer minimum masses of the parent body
population between 0.004 of the Earth's mass and 0.06 of the Earth's mass.
  We estimate grain production rates of 10 Gg/s around lambda Boo and HR 1570;
selective accretion of this matter may help explain their peculiar surface
abundances. There appear to be inner truncations in the dust clouds at 48 AU,
11 AU, 52 AU and 54 AU around HR 333, HR 506, HR 1082 and HR 3927,
respectively.
