biostudies-literatureUnknown10(1)Tollefsen EGlendonites have been found worldwide in marine sediments from the Neoproterozoic Era to the Quaternary Period. The precursor of glendonite, ikaite (CaCO₃ · 6H₂O), is metastable and has only been observed in nature at temperatures <7 °C. Therefore, glendonites in the sedimentary record are commonly used as paleotemperature indicators. However, several laboratory experiments have shown that the mineral can nucleate at temperatures>7 °C. Here we investigate the nucleation range for ikaite as a function of temperature and pH. We found that ikaite precipitated at temperatures of at least 35 °C at pH 9.3 -10.3 from a mixture of natural seawater and sodium carbonate rich solution. At pH 9.3, we observed pseudomorphic replacement of ikaite by porous calcite during the duratiScientific reports8141https://www.ebi.ac.uk/biostudies/studies/S-EPMC7235076biostudies-literatureIkaite nucleation at 35 °C challenges the use of glendonite as a paleotemperature indicator.PMC7235076Skelton ABruchert VLee CCTollefsen EBalic-Zunic TMorth CMfalseIkaite nucleation at 35 °C challenges the use of glendonite as a paleotemperature indicator.Glendonites have been found worldwide in marine sediments from the Neoproterozoic Era to the Quaternary Period. The precursor of glendonite, ikaite (CaCO₃ · 6H₂O), is metastable and has only been observed in nature at temperatures <7 °C. Therefore, glendonites in the sedimentary record are commonly used as paleotemperature indicators. However, several laboratory experiments have shown that the mineral can nucleate at temperatures>7 °C. Here we investigate the nucleation range for ikaite as a function of temperature and pH. We found that ikaite precipitated at temperatures of at least 35 °C at pH 9.3 -10.3 from a mixture of natural seawater and sodium carbonate rich solution. At pH 9.3, we observed pseudomorphic replacement of ikaite by porous calcite during the durati2020-01-01T00:00:00Z2020 May2025-04-19T14:25:17.28Z2020-05-30T07:04:46ZS-EPMC72350763242417310.1038/s41598-020-64751-5