astrophyllite

Astrophyllite is a very rare, brown to golden-yellow hydrous potassium iron titanium silicate mineral. Belonging to the astrophyllite group, astrophyllite may be classed either as an inosilicate, phyllosilicate, or an intermediate between the two. It forms an isomorphous series with kupletskite, to which it is visually identical and often intimately associated. Astrophyllite is of interest primarily to scientists and collectors.

Key facts

Mineral.name: Astrophyllite
Mineral.category: Inosilicates Astrophyllite group
Mineral.image: Astrophyllite-168179.jpg
Mineral.formula: (K,Na)3(Fe++,Mn)7Ti2Si8O24(O,OH)7
Mineral.IMAsymbol: Ast
Mineral.strunz: 9.DC.05
Mineral.system: Triclinic
Mineral.class: Pinacoidal () (same H-M symbol)
Mineral.symmetry: A
Mineral.color: Golden brown to yellow; rarely greenish
Mineral.habit: Tabular to bladed, radiating, stellate aggregates; lamellar masses
Mineral.cleavage: Perfect on [001] imperfect on [100]
Mineral.fracture: Uneven
Mineral.mohs: 3–4
Mineral.luster: Greasy, pearly, sub-metallic
Mineral.refractive: nα = 1.680 nβ = 1.700 nγ = 1.730
Mineral.opticalprop: Biaxial positive
Mineral.birefringence: 0.050

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Wikidata facts

Image: Astrophyllite-224740.jpg

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Nickel-Strunz '10th ed', review of (9th ed/ 2009 update): 9.DC.05
Commons category: Astrophyllite
Nickel-Strunz 9th edition (updated 2009): 9.DC.05
IMA Mineral Symbol: Ast
chemical formula: K₂NaFe²⁺₇Ti₂Si₈O₂₈(OH)₄F
Strunz 8th edition (series ID, updated): VIII/D*.05

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Heavy, soft and fragile, astrophyllite typically forms as bladed, radiating stellate aggregates. It is this crystal habit that gives astrophyllite its name, from the Greek words astron meaning "star" and phyllon meaning "leaf". Its great submetallic gleam and darkness contrast sharply with the light (felsic) matrix the mineral is regularly found within. Astrophyllite is usually opaque to translucent, but may be transparent in thin specimens.