Minerals of New York's Lockport Formation
The Lockport Formation extends into New York for 320 kilometers (200 miles) from Niagara County to Herkimer County. The rocks are of Middle Silurian age, about 420 million years old, and up to 61 meters (198 feet) thick. The Lockport Formation is predominantly dolostone with some shale.
The rocks formed from marine sediments that were deposited within the tidal zone and then briefly exposed to erosion above sea level. Some minerals of the exposed sediments were dissolved by rain water leading to the formation of cavities. The rocks were then buried to a depth of five kilometers(three miles). At that depth, a hot brine of about 170C (338F) invaded the cavities.
This solution, three to seven times saltier than sea water, deposited a remarkable suite of minerals. The brine carried calcium, magnesium, strontium, lead, zinc, fluorine, and sulfur that formed calcite, gypsum, dolomite, celestine, galena, sphalerite, and fluorite.