Context : Protoplanetary disks , interstellar clouds , and active galactic nuclei , contain X-ray dominated regions .
X-rays interact with the dust and gas present in such environments .
While a few laboratory X-ray irradiation experiments have been performed on ices , X-ray irradiation experiments on bare cosmic dust analogs have been scarce up to now .

Aims : Our goal is to study the effects of hard X-rays on cosmic dust analogs via in-situ X-ray diffraction .
By using a hard X-ray synchrotron nanobeam , we seek to simulate cumulative X-ray exposure on dust grains during their lifetime in these astrophysical environments , and provide an upper limit on the effect of hard X-rays on dust grain structure .

Methods : We prepared enstatite ( MgSiO _ { 3 } ) nanograins , analogs to cosmic silicates , via the melting-quenching technique .
These amorphous grains were then annealed to obtain polycrystalline grains .
These were characterized via scanning electron microscopy ( SEM ) and high-resolution transmission electron microscopy ( HRTEM ) before irradiation .
Powder samples were prepared in X-ray transparent substrates and were irradiated with hard X-rays nanobeams ( 29.4 keV ) provided by beamline ID16B of the European Synchrotron Radiation Facility ( Grenoble ) .
X-ray diffraction images were recorded in transmission mode and the ensuing diffractograms were analyzed as a function of the total X-ray exposure time .

Results : We detected the amorphization of polycrystalline silicates embedded in an organic matrix after an accumulated X-ray exposure of 6.4 \times 10 ^ { 27 } eV cm ^ { -2 } .
Pure crystalline silicate grains ( without resin ) did not exhibit amorphization .
None of the amorphous silicate samples ( pure and embedded in resin ) underwent crystallization .
We analyzed the evolution of the polycrystalline sample embedded in an organic matrix as a function of X-ray exposure .

Conclusions : Loss of diffraction peak intensity , peak broadening , and the disappearance of discrete spots and arcs , revealed the amorphization of the resin embedded ( originally polycrystalline ) silicate sample .
We explore the astrophysical implications of this laboratory result as an upper-limit to the effect of X-rays on the structure of cosmic silicates .