In their GSA Bulletin article published online last week, Timothy A. Goudge and colleagues detail the clay mineralogy of sediment from Lake Towuti, Indonesia, using a technique called visible to near-infrared (VNIR) spectroscopy. VNIR measures the signature of reflected light from a sample across a larger wavelength range than just visible light. At Lake Towuti, the spectral record shows distinct variations in clay mineralogy over the past 40,000 years.