Glendonites, pseudomorphs after marine sedimentary ikaite, are found throughout the Lower Cretaceous succession of Svalbard. Existing models for the ikaite-to-glendonite transformation do not explain the different petrological fabrics observed in the glendonites of Lower Cretaceous Svalbard. This study presents an improved model for the formation of these glendonites, based on petrographic and geochemical observations, and published work on ikaite breakdown. We show that for the glendonites of Lower Cretaceous Svalbard, methane is unlikely to be the sole or indeed main driver behind their formation, and present an improved model for their formation that accounts for the varied petrographic fabrics observed in these particular glendonites. Coupled with our new model, stable isotope data demonstrate why bulk samples of ancient glendonite cannot be used for palaeotemperature reconstructions.