Mineralogy of Two Fine‐Loamy Hydrosequences in South‐Central Michigan

This study was conducted to determine the effect of natural drainage on sand‐, silt‐, and day‐size minerals in two fine‐loamy hydrosequences in south‐central Michigan. Depths to water tables were monitored using piezometers during a 4‐yr period. Minerals in the dominant sand fraction were identified with a petrographic microscope. Minerals in the silt and clay fractions were identified and semiquantified using x‐ray diffraction. The predominant sand‐size mineral was quartz, with lesser amounts of potassium‐feldspars, plagioclase, sericite (altered muscovite) and dolomite. Silt fractions were composed dominantly of quartz with small amounts of feldspars and dolomite. Weathering of minerals in the sand and silt fractions appeared to be hindered by water saturation. The clay fraction was composed dominantly of mica, vermiculite, and kaolinite, with lesser amounts of chlorite, smectite, quartz, and feldspars. Transformation of mica to vermiculite or hydroxy interlayered vermiculite was the primary weathering sequence in the soils. Transformation of mica to smectite through interstratified vermiculite‐smectite occurred in one of the poorly drained pedons. Saturation apparently impeded the intensity of weathering. Most of the trioctahedral chlorite appeared to have completely dissolved or decomposed to soluble products in the A and B horizons.