Abstract Pedogenic siderite is a carbonate mineral that forms in the reducing groundwaters of poorly drained soils and paleosols in zonal climatic belts with strongly positive precipitation–evaporation balances. Microcrystalline and spherulitic forms of siderite are commonly recognized in micromorphologic studies of hydromorphic paleosols. Ancient paleosol sphaerosiderites commonly occur with diameters in excess of 1 mm, while modern pedogenic siderite crystal dimensions in excess of 100 µm are rare. Pedogenic siderites have been widely reported from Late Paleozoic, Mesozoic, and Cenozoic paleosols. The carbon and oxygen isotopic compositions of pedogenic siderites have been widely used as proxies for the oxygen isotopic composition of paleoprecipitation for their respective paleosols. Modern process studies of historic pedogenic siderites are yielding a more refined understanding of the stable isotopic systematics of low-temperature siderite. These works will lead to a future change in usage of published siderite–water 18 O fractionation equations.

Abstract The scientific literature is replete with reported observations of bacteria on rocks, in rocks, around rocks, precipitating rocks, and dissolving rocks in both ancient and modern systems, and this is an active and growing area of research. Many of these studies rely on scanning electron microscopy (SEM) to image mineral surfaces and to show a link between the presence of microorganisms and a particular geochemical process such as weathering or mineral precipitation. The ability of a researcher to show this link, however, will be governed by the quality and interpretation of the image, and the recognition of imaging artifacts and the shortcomings of using SEM as a sole method of investigation. The purpose of this chapter is to provide basic guidelines and procedures for collecting, preserving and processing mineral samples for SEM imaging, and the use of biomass determination and fluorescence in situ hybridization (FISH) analysis of microorganisms attached to rocks to augment SEM image analysis. This is not a review of the existing literature, rather it is a report of the methods that we have found useful in characterizing microbes on rocks. For basic SEM technique, general texts are available (e.g., Goldstein et al., 1992 ). We have similarly not included a discussion of transmission electron microscopy (TEM) methods, which is another tool that can be used to examine microbe-mineral interactions at very high magnification.