Kentrolite

Formula:  Pb₂Mn₂Si₂O₉

Origin of name:  From Greek for spike

Crystal system:  Orthorhombic

Crystal class:  2/m 2/m 2/m

Twinning: 

Unit cell: 

Colour:  Dark reddish brown; black on surface

Diaphaneity: 

Luster:  Vitreous to submetallic, greasy, dull

Habit:  Crystals prismatic, minute, may have sheaf-like form; massive

Hardness:  5

Specific gravity:  6.2

Cleavage:  1; {110} distinct

Tenacity: 

Streak:  Yellowish brown

Synonyms/varieties:

Comments:  Series with melanotekite