Mineral Information and Data:

Bannisterite
(Ca,K,Na)(Mn2+,Fe2+)10(Si,Al)16O38(OH)8 • nH2O [CNMNC approved formula]

Named for Dr. Frederick Allen Bannister (1901-?), formerly Keeper of Minerals, British Museum (Natural History), London, England.

IMA status : Approved Species 1968 (IMA1967-005)
CLASSIFICATION 
Dana
(8th edition) :
74.01.01.04  
  (74) Phyllosilicate Modulated Layers
  (74.01) with joined islands
  (74.01.01) Stilpnomelane group
  
Nickel-Strunz
(10th edition) :
09.EG.75
  (09) Silicates
  (09.E) Phyllosilicates
  (09.EG) Double nets with 6-membered and larger rings
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 22.26Å, b = 16.36Å, c = 24.66Å; β = 94.28°
Crystal Habit: As prismatic bladed crystals and aggregates, to 20 cm; as anhedral plates bounded by cleavage surfaces.
  
Color: Light to dark brown, black
Diaphaneity: Translucent
Luster: Resinous
Hardness (Mohs): 4
Measured Density: 2.83 - 2.84 g/cm3
Cleavage: Perfect on {001}; a second prismatic cleavage is noted microscopically.
  
Geologic Setting: In metamorphosed Mn-Zn orebodies.
Mineral Association: Manganoan and zincian amphiboles, rhodonite, sphalerite, quartz, calcite, barite (Franklin, New Jersey, USA); rhodonite, sphalerite, fluorite, galena, apophyllite, quartz (Broken Hill, Australia)
  

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