  The presence or absence of ice in protoplanetary disks is of great importance
for the formation of planets. By enhancing the solid surface density and
increasing the sticking efficiency, ice catalyzes the rapid formation of
planetesimals and decreases the time scale for giant planet core accretion.
Aims: In this paper we analyse the composition of the outer disk around the
Herbig star HD~142527. We focus on the composition of the water ice, but also
analyse the abundances of previously proposed minerals. Methods: We present new
Herschel far infrared spectra and a re-reduction of archival data from the
Infrared Space Observatory (ISO). We model the disk using full 3D radiative
transfer to obtain the disk structure. Also, we use an optically thin analysis
of the outer disk spectrum to obtain firm constraints on the composition of the
dust component. Results: The water ice in the disk around HD~142527 contains a
large reservoir of crystalline water ice. We determine the local abundance of
water ice in the outer disk (i.e. beyond 130\,AU). The re-reduced ISO spectrum
differs significantly from that previously published, but matches the new
Herschel spectrum at their common wavelength range. In particular, we do not
detect any significant contribution from carbonates or hydrous silicates, in
contrast to earlier claims. Conclusions: The amount of water ice detected in
the outer disk requires $\sim80\,$\% of the oxygen atoms. This is comparable to
the water ice abundance in the outer solar system, in comets and in dense
interstellar clouds. The water ice is highly crystalline while the temperatures
where we detect it are too low to crystallize the water on relevant time
scales. We discuss the implications of this finding.
