- Mansons Mine, Bucks County, Pennsylvania, United States1
- Maryland1
- Maryland, United States1
- Massachusetts1
- Matlock, Derbyshire, England, United Kingdom1
- McNamee Mine, Bath, Aiken County, South Carolina, United States1
- Mediterranean1
- Middletown, Middlesex County, Connecticut, United States1
- Midland, Cabarrus County, North Carolina, United States1
- Milos, Nisos, Cyclade Islands, Aegean Islands, Greece1
- Mississippi River1
- Montclair, Essex County, New Jersey, United States1
- Monte Rose, Liguria, Italy1
- Mount Holyoke, Hampshire County, Massachusetts, United States1
- Mount Vesuvius, Napoli province, Campania, Italy1
- Mt. Etna, Sicily, Italy1
- Nashville, Davidson County, Tennessee, United States1
- Neidermennig, Rheinland, Germany1
- Neshaminy Creek, Philadelphia County, Pennsylvania, United States1
- New Almaden District, Santa Cruz Mountains, Santa Clara County, California, United States1