Pyrolusite

Physical Properties
Chemical formula MnO2
Class Oxide
Crystal system Tetragonal
Habit Perfect tetragonal prisms (rare)
Dendritic
Fibrous
Reniform
Columnar
Orthorhombic pseuodmorphs after manganite
Color Black
Hardness 1 to 2
Specific gravity 4.5 to 5
Cleavage Perfect prismatic {110} (rare)
Fracture Uneven
Luster Metallic
Transparency Opaque
Streak Black
after Perkins, 373

Pyrolusite in Hand Sample

Pyrolusite in hand sample

Further Reading

Pyrolusite at webmineral.com

Pyrolusite at mindat.org