FLUORESCENT SODALITE IN SEDIMENT ALONG THE SOUTHERN SHORES OF THE GREAT LAKES FROM MICHIGAN TO NEW YORK

Geology enthusiasts searching the beaches along the southern shores of Lake Superior often uncover small amounts of pebble to cobble sized sediment with a syenite mineralogy that includes significant amounts of fluorescent sodalite. These rocks, informally referred to as ‘yooperlites’, primarily fluoresce a distinctive orange-red under short wave UV light. Similar sediment has recently been identified along the shorelines of Lake Erie and Lake Ontario in New York; petrographic and chemical analysis of these sediment indicate a comparable mineralogy and chemistry to “genuine yooperlites”. Each contain large quantities of albite, alkali and potassium feldspars, as well as both large and small phenocrysts of the fluorescent sodalite. Iron-sodium rich pyroxene and amphibole were also present in all samples, though there seem to be some modal differences between sample locations by state. While seemingly concentrated on the southern shores of the Great Lakes, it is not clear that this sediment is sourced from or reflects the geology of local bedrock in Michigan or New York.

If this sediment did not originate at their sample locations, it may have been transported southward by fluvial or glacial processes. Potential sources of these rocks exist in Ontario, but it is not apparent that they originated and were eroded from there. Constraining the original source and extent of deposition of this sediment could help inform about its weathering, transport history, and potentially contribute to a better understanding of water, ice, and sediment movement through the Great Lakes Basin. Because of the simplicity of identifying sodalite by means of UV light, the distribution of this sediment could effectively be mapped to a great extent by means of educational outreach or citizen science activities spread over a large geographical area. Activities incorporating searching and identifying this sediment can be applied in a variety of settings and involve a diversity of participants regardless of age, ability, or scientific background.