Mineralogic composition of cryogenic evaporites determined by low-temperature X-ray diffactometry


As part of a collaborative investigation between researchers at Rice University, Arkansas State University, University of Rochester, and Ohio State University, lakes of the McMurdo Dry Valleys were sampled at discreet depth intervals during the 2005-2006 field season.  Sample splits were subsequently analyzed for chemical and isotopic composition of both gases and dissolved  ions, as well as dissolved organic carbon. In addition, cryogenic salts were sampled in the surrounding lake shores in order to determine the salt sources. Gravity cores were also obtained and in the case of Lake Vanda, a white precipitate was recovered from the lake bottom.  
Presented  in this file is the mineralogic composition of salt crusts that were collected on the surface of sediment and rocks surrounding the lakes, as well as the lake-bottom precipitate from Lake Vanda.  The results are based on low-temperature XRD determinations, and Rietveld refinement of whole peaks.

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 Salts were collected in the areas surrounding the Dry Valley lakes. The samples were bagged and then placed either in boxes or in plastic containers in order to avoid crushing them. The samples were stored in a freezer at -40 C, prior to shipping, due to the instability of Antarcticite at room temperatures. The samples were then shipped under dry ice to Rice University in Houston, then shipped to the Steacie Institute for Molecular Sciences  in Ottawa, which is a division of the Canadian Research Council.  
Hailong Lu, a research scientist in the Institute whose specialty is on the structure of marine gas hydrates, placed each sample in a mortar with liquid nitrogen and then ground it into a powder. The powders were then analyzed with a low-temperature XRD. Temperatures were first dropped to -140 C, then gradually  ramped up to room temperature to look at phase changes that occurred on warming. Minerals were identified JADE 8.5 data processing software, and the ICDD PDF-2 Data Base. The relative abundance of each crygenic mineral was dertermined by the Rietveld method of whole-peak fitting.

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Metadata completed in 2016

This dataset was created Oct 1, 2008 by MCM-LTER information manager (Chris Gardner) after email discussion with PI Glen Snyder.

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This material is based upon work supported by the National Science Foundation under Grant No.0440686


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