Cement-making and the mining of limestone and gypsum for Portland Cement are major exports of the area. Charlevoix's Medusa Cement Plant was bought by Cemex in the 1990s. Alpena is home to the Lafarge Company's holdings in the world's largest cement plant and is home to Besser Block Co. (Jesse M. Besser invented concrete block in 1904 and founded the Besser Block Co. in Alpena after making the concrete block making machine). USG Corporation, also known as United States Gypsum Corporation, operates several quarries, including one at Alabaster, and one in Rogers City. Rogers City is the locale of the world's largest limestone quarry, which is also used in steel making all along the Great Lakes.