Mineral Information and Data:

Annite
KFe2+3(Si3Al)O10(OH)2 [CNMNC approved formula]

Named for the first noted occurrence at Cape Ann, Massachusetts, USA.

IMA status : Approved Species 1863 ()
CLASSIFICATION 
Dana
(8th edition) :
71.02.02b.03  
  (71) Phyllosilicate Sheets of Six-Membered Rings
  (71.02) with 2:1 Layers
  (71.02.02b) Mica Group (Biotite subgroup)
  
Nickel-Strunz
(10th edition) :
09.EC.20
  (09) Silicates
  (09.E) Phyllosilicates
  (09.EC) Phyllosilicates with mica sheets, composed of tetrahedral and octahedral nets
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 5.386 Å, b = 9.324 Å, c = 10.268 Å, b = 100.63°
Crystal Habit: Tabular crystals and foliated masses, cleavage fragments with pseudo-hexagonal outlines
Twinning: Contact twins with composition surface {001} and twin axis [310]
  
Color: Black, greenish brown, red
Diaphaneity: Translucent to transparent
Luster: Adamantine, vitreous
Hardness (Mohs): 2.5 - 3
Measured Density: 3.3 g/cm3
Cleavage: 1; {001} perfect
Tenacity: Flexible
Streak: Brownish white
  
Polymorphism and Series: 1M polytype.
Geologic Setting: In magnesium-poor igneous and metamorphic rocks
Mineral Association: Fluorite, zircon (Rockport, Massachusetts, USA)
  

 

Annite
Black mica (annite)
Origin: Mont Saint-Hilaire, Rouville RCM, Montérégie, Québec, Canada
Photo: © Rruff Project

 

Annite
Bottle-green manganoan annite
Origin: A4 highway tunnel, Thiemendorf, Königshain,
Oberlausitz, Saxony, Germany
Picture size: 2.5 mm
Photo and Owner: Thomas Witzke

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