This data release contains macro and microscale datasets describing the abundance, valence states, and mineral residence(s) of chromium, iron, and manganese in natural and synthetic mineral mixtures used in laboratory experiments designed to simulate dynamic conditions in an engineered aquifer system [see Izbicki and Groover (2018) and Miller and others (2020)]. The landing page contains primary metadata about this release and an overview "sample information" table containing descriptions of samples, their analyses, and their methods of preparation and preservation. As there is not a one-to-one correlation between samples and types of analyses performed, the overview table is an important navigation tool to locate data associated with specific samples. Data are grouped into three child pages: the first contains qualitative multi-element compositional data from scanning electron microscopy-energy dispersive spectrometry. The normalized data are in the form of element maps and tables of compositional data from spots or areas. These qualitative data are accompanied by backscattered electron images and, in some cases, corresponding optical images. Tabulation of quantitative measurements of features in a subset of the optical images is also presented. The second child page contains bulk chemical data of three types: (a) qualitative multi-element compositional data from portable X-ray fluorescence spectrometry; (b) quantitative multi-element compositional data from chemical-digestion followed by inductively-coupled plasma- optical emission or inductively-coupled plasma-mass spectrometry; and (c) quantitative total organic carbon data. The third child page contains (a) bulk synchrotron-based X-ray absorption spectra; (b) microbeam synchrotron-based X-ray fluorescence maps and spectra; and (c) microbeam Raman spectra (and corresponding optical images). This release contains all solid-phase data relevant to interpretations, graphs, and figures in the report entitled "Sequestration and Reoxidation of Chromium in Experimental Microcosms" (Miller and others 2023), to be published as Chapter J in a USGS Professional Paper (Izbicki and others, 2023). Data collected after July 22, 2019 are subject to secondary data review as required by the Energy and Minerals Mission Area Quality Management System (EMMA QMS). As this process is not yet complete, all data in this release collected after July 22, 2019 must be considered preliminary or provisional (subject to revision). They are being provided to meet the need for timely best science. The data have not received final approval by the U.S. Geological Survey (USGS) and are provided on the condition that neither the USGS or the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the data. When the secondary data review is complete, this provisional statement will be removed. Further details are given on each childs page.