Mineral Information and Data:

Astrophyllite
K2NaFe2+7Ti2(Si4O12)2O2(OH)4F [CNMNC approved formula]

Named from the Greek άστρον ("astron") for "star" and φύλλον ("phyllon") for "leaf", in allusion to its habit of starburst-like sprays and micaceous cleavage.

IMA status : Valid species (Pre-IMA 1854) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
69.01.01.01  
  (69) Inosilicate Chains with Side Branches or Loops
  (69.01) with (P=2, and N=4, 2 branches)
  (69.01.01) Astrophyllite group
  
Nickel-Strunz
(10th edition) :
09.DC.05
  (09) Silicates
  (09.D) Inosilicates* Structural terminology per Liebau (1985)
  (09.DC) with branched 2-periodic single chains; Si2O6 + 2SiO3 Si4O12
  
Crystal system: Triclinic System
Point group (H-M): 1 — pedial
Unit cell: a = 11.76Å, b = 5.36Å, c = 21.08Å α = 90°, β = 94°, γ = 90°
Crystal Habit: Crystals tabular perpendicular to {001}, bladed or acicular, some faces commonly striated, to 10 cm; groups may be stellate.
  
Color: Bronze-yellow to gold-yellow, brown to reddish brown.
Diaphaneity: Opaque to translucent in thin leaves
Luster: Submetallic, pearly, greasy
Hardness (Mohs): 3
Measured Density: 3.2 - 3.4 g/cm3
Cleavage: Perfect on {001}, poor on {100}
Tenacity: Brittle
Streak: Golden
  
Geologic Setting: In nepheline syenites, alkali granites, and their pegmatites; less commonly in fenites and other metasomatized rocks; in nepheline syenite gneisses and paragneisses.
Mineral Association: Albite, aegirine, arfvedsonite, nepheline, natrolite, zircon, biotite, leucophanite, eudialyte, catapleiite, djersherite, rasvumite, delhayelite, kupletskite.
  

 

Astrophyllite
Brown bladed astrophyllite crystals with riebeckite in matrix
Origin: Monte Galineiro, Vigo, Pontevedra Province, Spain
Sample size: 6 x 7 cm
Photo: Diederik Visser

 

Astrophyllite
(zoom-in of above)

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