  This is the first paper in a series of three where we present the first
comprehensive inventory of solid state emission bands observed in a sample of
17 oxygen-rich circumstellar dust shells surrounding evolved stars. The data
were taken with the Short and Long Wavelength Spectrographs on board of the
Infrared Space Observatory (ISO) and cover the 2.4 to 195 micron wavelength
range. The spectra show the presence of broad 10 and 18 micron bands that can
be attributed to amorphous silicates. In addition, at least 49 narrow bands are
found whose position and width indicate they can be attributed to crystalline
silicates. Almost all of these bands were not known before ISO. We have
measured the peak positions, widths and strengths of the individual, continuum
subtracted bands. Based on these measurements, we were able to order the
spectra in sequence of decreasing crystalline silicate band strength. We found
that the strength of the emission bands correlates with the geometry of the
circumstellar shell, as derived from direct imaging or inferred from the shape
of the spectral energy distribution. This naturally divides the sample into
objects that show a disk-like geometry (strong crystalline silicate bands), and
objects whose dust shell is characteristic of an outflow (weak crystalline
silicate bands). All stars with the 33.6 micron forsterite band stronger than
20 percent over continuum are disk sources. We define spectral regions (called
complexes) where a concentration of emission bands is evident, at 10, 18, 23,
28, 33, 40 and 60 micron. We derive average shapes for these complexes and
compare these to the individual band shapes of the programme stars.
