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Insights on Structure and Threshold Detection Limits of Stichtite (Magnesium-Chromium Carbonate-Hydroxide) by Fourier Transform Infrared Analysis

1
Department of Geological Sciences, California State University of San Bernardino, 5500 University Parkway, San Bernardino, CA 92407, USA
2
Department of Earth and Planetary Sciences, University of California Riverside, 900 University Avenue, Riverside, CA 92521, USA
*
Author to whom correspondence should be addressed.
Minerals 2020, 10(3), 215; https://doi.org/10.3390/min10030215
Received: 23 January 2020 / Revised: 23 February 2020 / Accepted: 25 February 2020 / Published: 28 February 2020
(This article belongs to the Section Crystallography and Physical Chemistry of Minerals)
Spectral features for natural stichtite at 1042, 1096, 1360, 1638, and 3482 cm−1 provide insights on mineral structure, with peaks consistent with OH stretching modes bound to Mg or Cr, CO32− antisymmetric stretches and CO32− bound within the sample and molecular water. These Infrared (IR) data suggest natural stichtite forms at a pH of >12 with increased water and decreased carbonate in the interlayer due to a smaller interlayer distance and unit cell. Higher pH favors lower divalent cation purity and may explain observed ranges of non-end member compositions in stichtite from localities around the world, and across geologic time. This constrains stichtite formation to a range of very high pH conditions and is consistent with active serpentinizing fluid vents and some mine wastes. IR has clear application for the detection and quantification of stichtite under field and laboratory conditions within the detection limits of 5% stichtite within a serpentine host. The size and grade of terrestrial stichtite deposits, and resolution of remote sensing instruments, suggest remote IR detection of stichtite is possible, and remote IR detection for Earth and Mars is discussed. View Full-Text
Keywords: Fourier transform infrared (FTIR); stichtite; serpentine; threshold detection; interlayer Fourier transform infrared (FTIR); stichtite; serpentine; threshold detection; interlayer
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Melchiorre, E.; Garcia, A.; Brounce, M. Insights on Structure and Threshold Detection Limits of Stichtite (Magnesium-Chromium Carbonate-Hydroxide) by Fourier Transform Infrared Analysis. Minerals 2020, 10, 215.

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