Formula: Mn⁴⁺O₂

Species:

Colour: black, steel-grey

Lustre: Sub-Metallic

Hardness: 3

Specific Gravity: 4.37

Crystal System: Orthorhombic

Member of: Ramsdellite Group

Name: Named in honor of Lewis Stephen Ramsdell (1895-1975), Professor of Mineralogy at the University of Michigan, who first described the mineral.

Type Locality: Lake Valley Mining District, Sierra County, New Mexico – USA

Forms by inversion of pyrolusite or oxidative dehydrogenation of groutite.