GLENDONITE, Calcite ps after ikaite, Henrietta, Tasmania, Australia

Glendonite, a captivating mineral pseudomorph located in Tasmania, is predominantly discovered in marine mudstones dating back to the Permian period. These distinctive star-shaped crystal formations initially originated from the mineral ikaite, which is known to form exclusively in near-freezing aquatic environments. As temperatures rose, the ikaite crystals either dissolved or expelled their water, transforming into calcite. Glendonites function as significant geological time capsules, providing tangible proof of ancient ice ages that occurred during the Permian period when Tasmania was a component of the supercontinent Gondwana.

Glendonites are the pseudomorphs of crystals and crystal clusters which grew in organic rich mud on the sea floor when the temperature was below 5 degrees Celsius. As the temperature rose and the original crystals dissolved, the space that they had occupied was colonised by harder minerals such as iron carbonate.

Ikaite is the mineral designation for the hexahydrate form of calcium carbonate, represented as CaCO3·6H2O. This mineral typically forms steep or spiky pyramidal crystals, which are often arranged radially and can vary in size from small thumbnail aggregates to large prominent spurs. Ikaite exists only in a metastable state and quickly decomposes by losing most of its water content when taken out of near-freezing water. This so-called "melting mineral" is more widely recognized through its pseudomorphs.

Although generally regarded as a rare mineral, its scarcity is likely attributed to the challenges associated with preserving samples. Ikaite was first identified in nature by the Danish mineralogist Pauly in the Ikka Fjord in southwest Greenland, near Ivittuut, which is known for its notable cryolite deposit.