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First Discovery of Dolomite and Magnesite in Living Coralline Algae and its Geobiological Implications

Created 17/10/2025

Updated 17/10/2025

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Dolomite is a magnesium rich carbonate mineral abundant in ancient coral reef formations [1-3] yet very little is found forming in modern sedimentary environments. For over 150 years this conundrum has led to various theories being put forward about dolomite formation, however none have solved the so called `Dolomite Problem'[1]. It has generally been considered a post-depositional diagenetic process [2, 3], despite little experimental success at replicating dolomite formation in normal sea water conditions [4]. Here we show dolomite is in fact forming with living crustose coralline algae Hydrolithon onkodes, a species growing prolifically in coral reefs globally. Chemical micro-analysis of the coralline skeleton reveals that not only are the cell walls calcitised, but that the cell spaces are typically filled with magnesite, rimmed by dolomite, or both. Thus there are at least three mineral phases present (magnesium calcite, dolomite and magnesite) rather than one or two (magnesium calcite and brucite) as previously thought[5-7]. Both the magnesium calcite and dolomite phases comprise a continuum of magnesium to calcium compositions, whereas magnesite is near ideal composition. Using a mass balance approach we quantify potential dolomitisation of the coralline algae and can account for the total amount of dolomite found in a raised Pleistocene reef [2]. Our results are consistent with observed dolomites in coralline-algal rich environments in fossil reefs. This is the first time the presence of dolomite in living coralline algae has been confirmed.

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Title First Discovery of Dolomite and Magnesite in Living Coralline Algae and its Geobiological Implications
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/01102047-f28e-4e0f-9f3f-e66139f7fab6
Contact Point
Geoscience Australia Data
clientservices@ga.gov.au
Reference Period 22/04/2018
Geospatial Coverage Australia
Data Portal Geoscience Australia

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This dataset was originally found on Geoscience Australia "First Discovery of Dolomite and Magnesite in Living Coralline Algae and its Geobiological Implications". Please visit the source to access the original metadata of the dataset:
https://ecat.ga.gov.au/geonetwork/srv/eng/csw/dataset/first-discovery-of-dolomite-and-magnesite-in-living-coralline-algae-and-its-geobiological-impli1