Calcite after Ikaite

specimen number:
2282073

location:
Carter Creek, Arctic Wildlife Refuge, North Slope, Alaska, USA

description:
Classic Alaskan pseudomorph specimen was sharp crystals of what were once ikaite in a cluster and now replaced by calcite. These are often referred to as glendonites. in good condition.

Carter Creek, located on the North Slope of Alaska within the Arctic National Wildlife Refuge, is a prominent geological outcrop locality rather than a commercial mining or quarrying operation. Geologically, the site serves as the type locality for the upper Oligocene Nuwok Member of the Sagavanirktok Formation, which dates back approximately 24 million years. The stratigraphy consists primarily of poorly consolidated marine sands, silty muds, and paper-thin laminated siliceous shales deposited in an ancient high-latitude coastal and shelf environment. Because the locality is protected within a national wildlife refuge, there has been no industrial mineral extraction, but the site has been evaluated through geological field expeditions and academic research since its initial discovery by petroleum and biostratigraphic geologists in the mid-1960s.

The locality is globally recognized for its abundant occurrences of glendonite, which are distinctive calcite pseudomorphs after the precursor mineral ikaite. Ikaite is a highly unstable calcium carbonate hexahydrate that precipitates exclusively in near-freezing, alkaline marine sediments with low oxygen and high organic content. As temperatures rise above four degrees Celsius or diagenetic conditions shift, the ikaite structure rapidly dehydrates and breaks down, losing its chemically bound water molecules and recrystallizing into a more stable, fine-grained gray to yellowish calcite aggregate. At Carter Creek, these pseudomorphs perfectly preserve the original, sharp crystal habits of the precursor ikaite, manifesting as impressive single blades up to six inches long or as large, multi-point radial clusters up to two feet in length that mimic a spiked pineapple or rosette formation.

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