  We report the detection of a feature at 65um and a broad feature around 100um
in the far-infrared spectra of the diffuse emission from two active
star-forming regions, the Carina nebula and Sharpless 171. The features are
seen in the spectra over a wide area of the observed regions, indicating that
the carriers are fairly ubiquitous species in the interstellar medium. A
similar 65um feature has been detected in evolved stars and attributed to
diopside, a Ca-bearing crystalline silicate. The present observations indicate
the first detection of a crystalline silicate in the interstellar medium if
this identification holds true also for the interstellar feature. A similar
broad feature around 90um reported in the spectra of evolved stars has been
attributed to calcite, a Ca-bearing carbonate mineral. The interstellar feature
seems to be shifted to longer wavelengths and have a broader width although the
precise estimate of the feature profile is difficult. As a carrier for the
interstellar 100um feature, we investigate the possibility that the feature
originates from carbon onions, grains consisting of curved graphitic shells.
Because of the curved graphitic sheet structure, the optical properties in the
direction parallel to the graphitic plane interacts with those in the vertical
direction in carbon onion grains. This effect enhances the interband transition
feature in the direction parallel to the graphitic plane in carbon onions,
which is suppressed in graphite particles. Simple calculations suggest that
carbon onion grains are a likely candidate for the observed 100um feature
carrier, but the appearance of the feature is sensitive to the assumed optical
properties.
