Glendonite is a unique and rare form of Calcite. It starts with Ikaite, a carbonate mineral that forms in near-freezing water. It is only found in a metastable state (barely stable), decomposing rapidly once removed from water, thus losing most of its water content. Referred to as a “melting mineral”, Ikaite can only survive as a pseudomorph (one mineral that chemically replaces another mineral without changing the external form of the original mineral). That’s where Calcite comes in, literally, completely replacing Ikaite while retaining the original crystalline form. This new transformation is now called Glendonite, a Calcite pseudomorph after Ikaite. Its colors include cinnamon-brown, orange-brown and pale brown, and its luster is earthy.

The crystal system for Glendonite is monoclinic, with very steep or spiky pryamidal crystals, often radially arranged, and of varying sizes from thumbnail to much larger size aggregates. 

Collectable specimens of this Calcite pseudomorph are found in limited localities, including Australia, Canada, Japan, Russia and the USA (California, Washington).