Gypsum

specimen number:
2292405

location:
Red River Floodway, Winnipeg, Manitoba, Canada

description:
A loose grouping of gemmy lustrous gypsum crystals. This is cleaved on the backside. Attractive and brightly fluorescent.

The Red River Floodway, a 30-mile-long flood-control channel wrapping around the east side of Winnipeg, Manitoba, was constructed between 1962 and 1968 to protect the city from the seasonal inundations of the Red River. The region sits atop the flat plain of glacial Lake Agassiz, a massive body of meltwater that covered the area at the end of the last Ice Age. Over thousands of years, as glaciers retreated, thick layers of fine-grained clay and silt accumulated on the lakebed. Within these Quaternary-age lake clays, sulfate-rich groundwater reacted with local carbonate sources to slowly crystallize gypsum. Excavation of the massive floodway channel sliced directly into these deep, wet clay layers, exposing highly abundant clusters and tinned, "duckbill-shaped" rosettes of clear, light-reactive gypsum that had been growing undisturbed underground.

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