FIG. 1.

(A) Stacked spectra in depth profile series showing a significant decrease in the band at 464 Δ cm⁻¹ assigned to the ν_sSi-O-Si symmetric stretching mode (A₁ symmetry mode) of α quartz, and the G band at 1600 Δ cm⁻¹ (assigned to a doubly degenerate TO and LO phonon mode corresponding to the E_2g2 mode of graphite with point group symmetry) and D band at 1350 Δ cm⁻¹ (a phonon mode that becomes Raman-allowed when defects are introduced to the lattice or decreasing dimension of crystallites occurs with A_1g symmetry) at a depth of 15 μm, and the data becoming unreliable at a depth of 20 μm. (B) Hyperspectral image generated from the intensity of the G band, D band, and A₁ band with increasing depth into thin section.