2.1" Stellate Glendonite (Calcite Pseudomorph) Cluster - Russia

Glendonite is not a mineral, but rather a calcite pseudomorph after ikaite (calcium carbonate hexahydrate). These mineral formations start out as crystalline masses of ikaite that form in near-freezing water of high alkalinity. At warmer temperatures, ikaite becomes unstable and loses its water content. It then converts to calcite, but retains its ikaite crystal structure.

The presence of glendonite in a succession of rocks is diagnostic evidence for the presence of glaciers in the geologic past. It occurs in three main morphologies: stellate glendonite, rosette glendonite, and bladed glendonite.