Ikaite, CaCO3 center dot 6H(2)O: Cold comfort for glendonites as paleothermometers

Neutron diffraction results are linked to the pre-diffraction, morphologica l crystallography of E.S. Dana to show that ikaite is the precursor of "gle ndonite" and "thinolite" and that some of the unusual features of the morph ology can easily be explained by an accidental near-equivalence of the unit cell of ikaite, CaCO3. 6H(2)O. This relationship between the morphology of the pseudomorphs and the crystallography of ikaite gives strong justificat ion for the use of "glendonite" as a paleothermometer, representing near fr eezing conditions for water.