  We report the first detection of ~10 and ~18 micron silicate dust emissions
in a low-luminosity active galactic nucleus (AGN), obtained in Spitzer-IRS 7-37
micron spectroscopy of the Type 1 LINER galaxy NGC3998. Silicate emissions in
AGN have only recently been detected in several quasars. Our detection counters
suggestions that silicate emissions are present only in the most luminous AGN.
The silicate features may be signatures of a dusty ``obscuring torus'' viewed
face-on as postulated for Type 1 AGN. However, the apparently cool (~200 K)
dust is inconsistent with theoretical expectations of much hotter torus walls.
Furthermore, not all Type 1 objects are silicate emission sources.
Alternatively, the silicate emission may originate in dust not directly
associated with a torus. We find that the long-wavelength (>20 micron) tail of
the emission in NGC3998 is significantly weaker than in the sample of bright
QSOs recently presented by Hao et al. The 10 micron profile in our NGC3998
spectrum is inconsistent with ``standard'' silicate ISM dust. This may indicate
differences in the dust composition, grain size distribution, or degree of
crystallization. The differences between NGC3998, QSOs, and Galactic templates
suggest that there are significant environmental variations.
