Determining the Composition of Interstellar Dust with Far-Infrared Polarimetry

Does interstellar dust come in distinct silicate and carbonaceous varieties, or are interstellar grains a homogeneous mishmash of different materials? We argue that sensitive dust polarimetry from ~100-850 μm can provide a definitive test, with implications ranging from the evolution of metals in the ISM to component separation in CMB experiments.