Backscatter electron microscopy of subaerial rock varnish reveals porous textures that are sites of cation leaching with lowered (K+ + Ca2+)/Ti4+ ratios and concentrations of manganese and iron. Laboratory studies show that rates of potassium and calcium leaching increase with temperature,time,and surface area, and decrease when varnish interdigitates with coatings of amorphous silica. Only varnishes with continuous layering should be used in paleoenvironmental research and paleomagnetic studies, not textures indicative of postdepositional modifications.

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