Dependence of optical properties on grain composition for silicate grains with cores made of aSil-1, aSil-2, aSil-3, and aSil-4 materials in pink, blue, green, and yellow, respectively (a_eff = 100 nm, oblate with e = 1.3) on the left and cores made of aSil-5, aSil-6, and aSil-7 in red, brown, and orange, respectively, on the right. Top: solid lines show Q_abs and dashed lines Q_sca. Middle: zoom in on the silicate mid-IR features. Bottom: ratios of Q_abs to THEMIS I.