Welcome to Pyramidia -- Online information repository for the pseudomorph known variously as Glendonite, Thinolite, Gennouishi, Hammer stone, Jarrowite, and Pyramidite. All of these are Calcite Pseudomorphs After Ikaite.

Glendonite forms as a result of the recrystallization or replacement of the original precursor mineral (Ikaite) with another mineral (Calcite). Ikaite incorporates water molecules while crystallizing, and can only form in very cold temperatures.

When the matrix encasing the ikaite crystals warms, as a result of ground movement or climate change, the Ikaite crystals collapse back into an aqueous solution, which then over time re-crystallizes as Calcite, filling the void left by the collapsed Ikaite and reproducing its form pseudomorphically. Cool huh!

The replacement pseudomorphs of Ikaite are variously named according to their locations, as follows:

Glendonites - Glendon, New South Wales, Australia
Thinolites - SW USA - Greek, thinos=shore
Jarrowites - Jarrow, UK
Fundylite - Bay of Fundy, Canada
Gennoishi - Japanese=hammerstones; Niigata Prefecture, Japan
Gersternkorner - German=barley-corn
Pyramidite - Pyramid Bay, North America
White Sea Hornets - Kola Penninsula, Russia