| Résumé | The term “glendonite” does not refer to a mineral, but to a class of pseudomorphs. A pseudomorph is a mineral that has taken the characteristic crystal shape of another mineral by processes such as replacement or recrystallization. Glendonites are pseudomorphs after the mineral ikaite, a monoclinic mineral with composition CaCO3·6H2O. Ikaite forms in near-freezing waters. It requires pressures exceeding those of the deepest ocean to be thermodynamically stable (Marland, 1975). Therefore when present in recent sediments it is always metastable. Ikaite may be “stabilized” by the presence of orthophosphate, an inhibitor of the precipitation of anhydrous CaCO3. There have been few observations of ikaite in nature, probably reflecting its rapid decomposition into water and CaCO3 when removed from cold waters. It may well be a rather common mineral. It appears to occur in two forms: as crystals (Suess et al., 1982), often in muddy sediment, and as massive tufa towers; e.g., Ikka Fjord,... |
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