# Astrophyllite

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{{Short description|Hydrous potassium iron titanium silicate mineral}}
{{Infobox mineral
| name        = Astrophyllite
| category    = [Inosilicates](/source/Inosilicates) <br />Astrophyllite group
| image       = Astrophyllite-168179.jpg
| caption     = 
| formula     = (K,Na)<sub>3</sub>(Fe<sup>++</sup>,Mn)<sub>7</sub><!--
                -->Ti<sub>2</sub>Si<sub>8</sub>O<sub>24</sub>(O,OH)<sub>7</sub>
|IMAsymbol=Ast<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref>
| molweight   = 
| strunz      = 9.DC.05
| system      = [Triclinic](/source/Triclinic)
| class       = Pinacoidal ({{overline|1}}) <br/><small>(same [H-M symbol](/source/H-M_symbol))</small>
| symmetry    = ''A''{{overline|1}}
| color       = Golden brown to yellow; rarely greenish
| habit       = Tabular to bladed, radiating, stellate aggregates; lamellar masses
| twinning    = 
| cleavage    = Perfect on [001] imperfect on [100]
| fracture    = Uneven
| mohs        = 3–4
| luster      = Greasy, pearly, sub-metallic
| refractive  = nα = 1.680 nβ = 1.700 nγ = 1.730 
| opticalprop = Biaxial positive
| birefringence = 0.050
| pleochroism = Strong: X= deep red-orange Y= orange-yellow Z= lemon-yellow
| streak      = Yellowish brown or white
| gravity     = 3.2–3.4
| density     = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| diaphaneity = Translucent to opaque
| other       = 
| references  = <ref name=Webmin>https://webmineral.com/data/Astrophyllite.shtml Webmineral</ref><ref name=Mindat>http://www.mindat.org/min-405.html Mindat</ref><ref name=Handbook>http://rruff.geo.arizona.edu/doclib/hom/astrophyllite.pdf Handbook of Mineralogy</ref>
}}

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

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

As the crystals themselves possess perfect cleavage, they are typically left ''in situ'', the entire aggregate often cut into slabs and polished. Owing to its limited availability and high cost, astrophyllite is seldom seen in an ornamental capacity. It is sometimes used in [jewellery](/source/jewellery) where it is fashioned into [cabochon](/source/cabochon)s.

Found in cavities and fissures in unusual felsic [igneous rock](/source/igneous_rock)s, astrophyllite is associated with [feldspar](/source/feldspar), [mica](/source/mica), [titanite](/source/titanite), [zircon](/source/zircon), [nepheline](/source/nepheline), and [aegirine](/source/aegirine). Common impurities include [magnesium](/source/magnesium), [aluminium](/source/aluminium), [calcium](/source/calcium), [zirconium](/source/zirconium), [niobium](/source/niobium), and [tantalum](/source/tantalum). It was first discovered in 1854 at its type locality; [Laven Island](/source/Laven_Island), [Norway](/source/Norway). Kupletskite was not known until 1956, over a hundred years later.

Astrophyllite is found in a few scarce, remote localities: [Mont-Saint-Hilaire](/source/Mont-Saint-Hilaire), [Quebec](/source/Quebec), [Canada](/source/Canada); [Pikes Peak](/source/Pikes_Peak), [Colorado](/source/Colorado), [US](/source/US); [Narsarsuk](/source/Narsarsuk) and [Kangerdluarsuk](/source/Kangerdluarsuk), [Greenland](/source/Greenland); Brevig, Norway; and the [Kola Peninsula](/source/Kola_Peninsula), [Russia](/source/Russia).

== See also ==
{{commons category|Astrophyllite}}
*[List of minerals](/source/List_of_minerals)
==References==
{{Reflist}}

Category:Iron(II) minerals
Category:Inosilicates
Category:Triclinic minerals
Category:Minerals in space group 2

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Adapted from the Wikipedia article [Astrophyllite](https://en.wikipedia.org/wiki/Astrophyllite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Astrophyllite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.