Mineral Information and Data:

Ferroglaucophane
[]Na2(Fe2+3Al2)Si8O22(OH)2 [CNMNC approved formula]

Named for its high ferrous iron content and similarity to glaucophane. First published in 1957. Redefined per nomenclature of amphiboles (IMA, 1997).

IMA status : Redefined IMA Approved; 1997 ()
CLASSIFICATION 
Dana
(8th edition) :
66.01.03c.02  
  (66) Inosilicate Double-Width Unbranched Chains, W=2
  (66.01) with P=2 amphibole configuration
  (66.01.03c) Group 4, the sodic amphiboles
  
Nickel-Strunz
(10th edition) :
09.DE.25
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DE) with 2-periodic double chains, Si4O11; Clinoamphiboles
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Space group: C2=m
Unit cell: a = 9.587Å, b = 17.832Å, c = 5.3Å β = 103.47°
Crystal Habit: Elongated prismatic crystals.
Twinning: Simple or multiple twinning || {100}
  
Color: Blue to bluish gray
Diaphaneity: Semitransparent
Luster: Vitreous
Hardness (Mohs): 6
Measured Density: 3.18 - 3.34 g/cm3
Cleavage: Perfect on {110}, intersecting at ~58° and ~122°
Tenacity: Brittle
Fracture: Conchoidal to uneven
  
Polymorphism and Series: Forms a series with glaucophane.
Geologic Setting: In metamorphic rocks of the high-pressure, low-temperature blueschist facies, commonly derived from either siliceous sedimentary, alkalic basaltic, or felsic volcanic predecessors
Mineral Association: Paragonite, lawsonite, albite, spessartine, almandine, epidote, omphacite
  

 

Ferroglaucophane
Ferroglaucophane crystals (size 4-12 mm) from Herin mine (TL).
Origin: Herin mine, Champdepraz, Aosta Valley, Italy
Photo and collection: Giovanni Fraccaro.

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