Figure 10. Diagram showing hypothetical structure of a lignin-derived organic molecule in a brown coal (lignite). This structure is based on studies using carbon-13 nuclear-magnetic-resonance (¹³C NMR) spectroscopy and other organic-geochemical methods such as those described in table 2. Lignin is one of the constituents of woody tissue found in all vascular plants, such as trees and shrubs (W.H. Orem, U.S. Geological Survey, written commun., 1997). Studying organic matter helps provide information about the plant sources of coal and, subsequently, coal quality. See figure 9 for chemical elements.