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November-December 2017

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Road-Cut Mineral Occurrences of St. Lawrence County, New York, Part 8: A Final Summary

THE BASEMENT ROCKS of St. Lawrence County are largely metamorphosed sediments (meta-sediments) of Precambrian age (more than 1.2 bya), intruded here and there by igneous rocks of various ages. Mineralization resulting in specimens of interest to collectors began during the Precambrian regional metamorphic events and continued intermittently to the present. A map showing all the localities that have yielded specimens in collections would contain a vast array of sites; therefore, one might expect that each time a road cut is excavated, interesting mineral specimens might be exposed. Although this is true, the probability of finding collectible minerals in new road cuts is much lower than might initially be expected. The relative rarity of productive road cuts, even in a richly mineralized region, reflects the rarity of crystallized minerals in the surface rocks of the earth generally, and specifically reflects the fact that most occurrences in St. Lawrence County have a small footprint. In other words, if the many dots on a county map showing mineral occurrences were transformed to areas of mineralization, the percentage of the total land area would still be very small. Nonetheless, road cuts occasionally expose richly mineralized zones of significance to the collecting community, and this was the rationale for this series of articles. 


Dr. Steven C. Chamberlain, a collector specializing in the minerals of New York State and a consulting editor of Rocks & Minerals, is coordinator of the Center for Mineralogy at the New York State Museum.

Michael R. Walter is an earth science and geology teacher and an active field collector of the minerals of upstate New York and Canada.

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