Omya Plant, Florence Omya is a worldwide processor of minerals for industrial purposes. The company’s first North American plant, located in Florence, began production in 1979. Production has increased over the years, with the facility expanded many times over. Limestone is shipped to the Omya plant from quarries throughout Vermont. The mineral leaves the plant in tank cars as calcium carbonate slurry, and is widely used across the country in agriculture and industry. April 27, 2016.