  We present IRS spectra and revised MIPS photometry for the 18 members of the
Eta Chamaeleontis cluster. Aged 8 Myr, the Eta Cha cluster is one of the few
nearby regions within the 5-10 Myr age range, during which the disk fraction
decreases dramatically and giant planet formation must come to an end. For the
15 low-mass members, we measure a disk fraction ~50%, high for their 8 Myr age,
and 4 of the 8 disks lack near-IR excesses, consistent with the empirical
definition of "transition'' disks. Most of the disks are comparable to
geometrically flat disks. The comparison with regions of different ages
suggests that at least some of the "transition" disks may represent the normal
type of disk around low-mass stars. Therefore, their flattened structure and
inner holes may be related to other factors (initial masses of the disk and the
star, environment, binarity), rather than to pure time evolution. We analyze
the silicate dust in the disk atmosphere, finding moderate crystalline
fractions (~10-30%) and typical grain sizes ~1-3 micron, without any
characteristic trend in the composition. These results are common to other
regions of different ages, suggesting that the initial grain processing occurs
very early in the disk lifetime (<1 Myr). Large grain sizes in the disk
atmosphere cannot be used as a proxy for age, but are likely related to higher
disk turbulence. The dust mineralogy varies between the 8-12micron and the
20-30 micron features, suggesting high temperature dust processing and little
radial mixing. Finally, the analysis of IR and optical data on the B9 star Eta
Cha reveals that it is probably surrounded by a young debris disk with a large
inner hole, instead of being a classical Be star.
