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What minerals or rocks are found in the Great Lakes region?
The primary rock exposed along the shore of Lake Ontario on both the US and Canadian shores in that area is an Ordovician age limestone about 400 million years old. Locally, it may contain some fairly large orthocone cephalopod fossils (including some that measure 6 feet in length!). This limestone is quarried both near Kingston, Ontario and in the Watertown, New York areas for crushed stone to be used in construction. Rarely, it may contain small veins that hold calcite crystals.
Further to the northeast in the Thousand Islands region lies an extension of the Canadian Shield known as the Frontenac Axis. This rock is mostly granitic gneiss and is about 1 billion years old (that's 1,000,000,000 years!).
There are many interesting, but small, pockets of other minerals in both these areas as well as in associated rocks that are inland from the St. Lawrence River on both sides of the border. Many on the Canadian side were worked for mica and apatite in the past, but are of no economic importance today. The only major economically valuable deposits still being worked in the area today are in the Balmat, New York district, where talc, wollastonite, and zinc are currently being mined.
The principal minerals found throughout the Great Lakes region include:
Thank you for your question!
Answered on June 19, 2001 and updated on July 5, 2001