Astrophyllite
Current inventory:  0 gems
 

  
Astrophyllite gets its name from the Greek word aster for star and fyllon for leaf in allusion to its habit of starburst-like sprays and micaceous cleavage.

Discovered in 1854;   IMA status: Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(K,Na)₃(Fe²⁺,Mn)₇Ti₂Si₈O₂₄(O,OH)₇

Potassium Sodium Iron Manganese Titanium Silicate Hydroxide

Molecular Weight:

1,289.00 gm

Composition:

Potassium

6.07 %

K

7.31 %

K₂O

Sodium

1.78 %

Na

2.40 %

Na₂O

Magnesium

1.41 %

Mg

2.35 %

MgO

Titanium

7.43 %

Ti

12.39 %

TiO₂

Manganese

4.26 %

Mn

5.50 %

MnO

Iron

22.75 %

Fe

29.26 %

FeO

Silicon

17.43 %

Si

37.29 %

SiO₂

Hydrogen

0.27 %

H

2.45 %

H₂O

Oxygen

37.86 %

O

Fluorine

0.74 %

F

0.74 %

F

-

- %

F

-0.31 %

-O=F₂

100.00 %

99.38 %

= TOTAL OXIDE

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/G.12-40

Nickel-Strunz 10th Ed. ID:

9.DC.05

9 : SILICATES (Germanates)
D : Inosilicates
C : Inosilicates with branched 2-periodic single chains; Si₂O₆ + 2SiO₃ Si₄O₁₂

Related to:

Astrophyllite Group. Astrophyllite-Kupletskite Series.

Members of Group:

Astrophyllite Group: Hydroastrophyllite, Kupletskite, Kupletskite-(Cs), Magnesioastrophyllite, Nalivkinite, Niobokupletskite, Niobophyllite, Zircophyllite.

Varieties:

None

Synonyms:

Aastrophyllite, Asterophyllite, Astrofillite

Crystal Data

Crystallography:

Triclinic - Pedial

Crystal Habit:

Crystals tabular, bladed or acicular, some faces commonly striated, to 10 cm; groups may be stellate.

Twinning:

None

Physical Properties

Cleavage:

Perfect on {001}, Poor on {100}

Fracture:

Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

3.0

Density:

3.20 - 3.40 (g/cm³)

Luminescence:

None

Radioactivity:

Barely Detectable; GRapi = 85.21 (Gamma Ray American Petroleum Institute Units)

Optical Properties

Color:

Bronze-Yellow to Gold-Yellow, Brown to Reddish Brown

Transparency:

Opaque to Translucent in thin leaves

Luster:

Sub-Metallic, Pearly, Greasy

Refractive Index:

1.678 - 1.758  Biaxial ( + )

Birefringence:

0.050

Dispersion:

Strong; r > v

Pleochroism:

Strong; X = deep orange-red; Y = orangeyellow; Z = lemon-yellow

Occurances

Geological Setting:

In nepheline syenites, alkali granites, and their pegmatites; less commonly in fenites and other metasomatized rocks; in nepheline syenite gneisses and paragneisses.

Common Associations:

Aegirine, Albite, Arfvedsonite, Biotite, Catapleiite, Delhayelite, Djerfisherite, Eudialyte, Kupletskite, Leucophanite, Natrolite, Nepheline, Rasvumite, Zircon

Common Impurities:

Nb, Ta, Zr, Al, Mg, Ca

Type Locality:

Langesundsfjorden, Larvik, Vestfold, Norway

Year Discovered:

1854

View mineral photos:

Astrophyllite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Astrophyllite is a rare titanium mineral that forms in beautiful radiating or star-like sheets with variable luster that can be nearly metallic in one specimen and pearly or greasy in another. Its colors range from coppery brown to bronze to reddish brown and can have bright flashes of yellow, gold, orange and red. Astrophyllite is typically opaque and therefore available only as cabochons. It takes on a very good shine and makes a beautiful gem.

The main sources of Astropyllite are Mont Saint-Hilaire, Québec, Canada; Narsaq, Kitaa (West Greenland) Province, Greenland; Langesundsfjorden, Larvik, Vestfold, Norway (Type Locality); San Miguel, Azores District (Azores Islands), Portugal; Kola Peninsula, Murmanskaja Oblast', Northern Region, Russia; St. Peters Dome, El Paso County, Colorado, USA
 

  
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