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Crystal
Habits of the Magnesium Hydroxide
Noreen A. Buster 1 Charles W. Holmes 2 Thomas J.
Goreau 3 Wolf Hilbertz, 2006, Crystal habits of the Magnesium Hydroxide mineral
Brucite within Coral Skeletons,
American Geophysical Union Annual Meeting, Abstract and Poster ABSTRACT The use of Magnesium/Calcium (Mg/Ca) ratios in coral skeletons as proxies of seasurface temperature (SST) and the overall fine-scale fluctuations in coral skeleton Mg/Ca data have been subjects of interest among coral scientists. More information is needed to define biomineralization and other processes taking place within the entire skeleton and within microenvironments of coral skeletons. Understanding how and where Mg is either incorporated into the skeleton or precipitated within voids of the skeleton is essential to answering the above questions and includes identifying individual influencing factors. Previously, we discovered and described physical locations and geochemical signatures of high-Magnesium brucite crystals throughout specific structures in skeletal coral Montastraea faveolata. Brucite was found to be concentrated within green bands that occur in some coral skeletons. These green bands are thought to be associated with a high-pH environment created by endolithic algae. Brucite has been identified in the skeletons of several genera of coral, and its existence provides information toward understanding the processes that take place within microenvironments of the carbonate skeleton, beneath the living surface of the coral. To follow up on previous studies, we compared the crystal habits of brucite found within the coral M. faveolata to brucite precipitated artificially in seawater using a cathode-array system. Samples were evaluated using a scanning electron microscope equipped with an energy dispersive spectrometer (EDS). As identified with photomicrographs, there are similar crystal habits between the two sample environments, including sphere-like clusters of rosettes, crystals forming a cylinder, loose rosettes. There are also different habits unique to each sample; however, the overall individual crystal form creating the rosette groupings is consistent. Semi-quantitative EDS spectra of both sample types show consistent high-Mg peaks. XRD analysis showed the artificially precipitated crystals to be brucite. Results from the coral skeleton crystals have proven difficult to obtain using XRD, but the crystals were determined to be brucite by infrared spectrometry. This study shows the similarity of brucite crystal habits between environments, and new XRD data from the electrically induced precipitates of brucite, reconfirming the existence of brucite within coral skeletons and contributing information about crystal habits of brucite previously not reported. |
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