  We present the first mid-IR detection of the linear polarization toward the
star CygOB2-12, a luminous blue hypergiant that, with Av of ~10 mag of
foreground extinction, is a benchmark in the study of the properties of dust in
the diffuse interstellar medium. The 8-13 micrometer spectropolarimetry,
obtained with the CanariCam multi-mode camera at the Gran Telescopio Canarias
(GTC), shows clear trends with wavelength characteristic of silicate grains
aligned in the interstellar magnetic field. The maximum polarization, detected
with 7.8 statistical significance near 10.2 micrometers, is (1.24 +/- 0.28) %
with position angle (126 +/- 8) deg. We comment on these measurements in the
context of recent models for the dust composition in the diffuse interstellar
medium.
