- Lyme Regis, Dorset County, England, United Kingdom1
- Macon County, Wilcox County, Alabama, United States1
- Magnet Cove, Hot Spring County, Arkansas, United States1
- Malacca, Malaysia1
- Manilla, Philippines1
- Mansons Mine, Bucks County, Pennsylvania, United States1
- Maryland1
- Maryland, United States1
- Massachusetts1
- Matlock, Derbyshire, England, United Kingdom1
- Mayesville, Sumter County, South Carolina, United States1
- Mazatlan, Mexico1
- McNamee Mine, Bath, Aiken County, South Carolina, United States1
- Medina, Orleans County, New York, United States1
- Meigs County, Portland, Ohio, United States1
- Mexico, Audrain County, Missouri, United States1
- Michigan, United States1
- Midland, Cabarrus County, North Carolina, United States1
- Milos, Nisos, Cyclade Islands, Aegean Islands, Greece1
- Mississippi River1