Figure 2

Raman map of a COM stone with orientation differences. (a) 5 µm spatial resolution map of COM with 1464 cm⁻¹ carboxylate stretch dominant. (b) 1 µm spatial resolution map of inset in (a). (c) 5 µm spatial resolution map of COM with 1491 cm⁻¹ carboxylate stretch dominant. (d) 1 µm spatial resolution map of inset in (c). (e) White light image. (f) 1 µm spatial resolution map of COD, inset from (e).