Gem library
Astrophyllite
Golden sprays in a star
Astrophyllite grows as golden blades radiating from a point, like a spray of sparks frozen in the rock. It is a mineral of rare alkaline rocks, and its beauty comes entirely from that geometry.
- Hardness (Mohs)
- 3 – 3.5
- Density
- 3.30 – 3.40
- Crystal system
- Triclinic
- Refractive index
- 1.678 – 1.733
- Cleavage
- Perfect on {001}
Mineralogical identity
- Family
- Silicates, inosilicates
- Species
- Astrophyllite
- Variety
- Astrophyllite on feldspar
- Chemical formula
- K₂Na(Fe,Mn)₇Ti₂Si₈O₂₆(OH)₄
- Crystal system
- Triclinic
- Classification
- Collector's mineral
- Rarity
- Rare
- Indicative price
- €1 – 30/ct
Etymology
From the Greek astron, «star», and phyllon, «leaf»: blades arranged in a star. The name is descriptive and perfectly accurate.
Physical & optical properties
- Hardness (Mohs)
- 3 – 3.5
- Density
- 3.30 – 3.40
- Refractive index
- 1.678 – 1.733
- Birefringence
- 0.055
- Cleavage
- Perfect on {001}
- Fracture
- Splintery
- Lustre
- Submetallic to pearly
- Diaphaneity
- Translucent to opaque
- UV fluorescence
- None
- Pleochroism
- Distinct
- Colours
- golden, bronze, brown, gold yellow
Formation, geology & history
A mineral of alkaline rocks
Astrophyllite forms only in one precise setting: nepheline syenites and alkaline pegmatites, igneous rocks poor in silica and rich in sodium, potassium, titanium and rare earths. Such massifs are few in the world, and the most famous are those of Khibiny and Lovozero, on the Kola peninsula in Russia, along with Ilímaussaq in Greenland. Astrophyllite crystallises there late, in the cavities, as flattened blades all starting from one seed. The ground is almost always a white to grey feldspar, sometimes a nepheline, and the contrast between the pale ground and the golden sprays is the whole interest of the polished plates.
A spray, and why it radiates
The star arrangement is not decorative, it is crystallographic. In a cavity, a single seed gives rise to blades each growing in a direction the structure permits, and since the mineral is triclinic, hence of minimal symmetry, the possible directions are many. The blades diverge, lengthen and end up forming a spray that occupies all the available space. The phenomenon has a name in mineralogy, radiating habit, and it is found in stibnite, wavellite or pyrophyllite, but rarely with such a metallic lustre.
Soft, and that is the limit
At hardness 3, astrophyllite is scratched by a coin, and its perfect cleavage makes it exfoliate like a mica. It is therefore never cut as a gem, and trade pieces are polished plates or domed cabochons where the blades come to the surface. Polishing is delicate: the blades and the feldspar around them do not have the same hardness, and too aggressive an abrasive hollows one and leaves the other in relief. The finest pieces come from Russia, where the material has been worked since the Soviet era. The titanium it contains has no industrial use here: the mineral is far too rare.
How to recognise it
- Radiating bladesElongated, flattened blades diverging from a point. If the flakes are scattered at random, it is biotite or a flake-bearing rock, not astrophyllite.
- Submetallic lustreBetween metal and pearl, very different from the matt gold of a pyrite or the bright gold of a copper flake. The blade returns light like a sheet of bronze.
- SoftnessA copper coin scratches a blade without effort. Any golden stone that resists steel is not astrophyllite.
Imitations, treatments & confusions
- Golden biotite sold as astrophylliteBiotite is a common golden-brown mica, but in flakes rather than sprays. The geometry settles it at once.
- Gilded glass or glitter resinOn cheap little cabochons. A homogeneous surface, identical flakes, no radiating structure.
- Reconstituted stoneFragments of astrophyllite set in a resin imitating feldspar. Under a loupe the ground is too uniform and has no crystalline grain.
Deposits & origins
Russia (Khibiny massif, Kola peninsula: the reference), Greenland (Narsarsuk), Norway (Låven, the type locality), Canada, United States (Colorado), China
Care & precautions
- No water: the perfect cleavage of the blades holds moisture and lifts them.
- A soft dry brush, following the direction of the blades.
- Never ultrasonics, which break the spray up.
- Store isolated and flat, everything scratches it and a broken blade cannot be glued back.
Traditions & crystal healing
- Chakras
- Solar plexus · crown
- Zodiac signs
- Leo · Scorpio
- Element
- Fire
The handbooks make it a stone of impetus and self-knowledge, playing on the image of the star. Its relative rarity has given it a reputation as a stone «for insiders» in lithotherapy circles. Cultural heritage, never medicine.
The virtues described here belong to tradition and cultural heritage. They are in no way medical advice and never replace a consultation.
Frequently asked questions
Astrophyllite or pyrite?
Pyrite is cubic, golden, hardness 6, and does not form sprays. Astrophyllite is in radiating blades and is scratched by a coin.
Can it be worn?
In a protected pendant only. At hardness 3 with perfect cleavage, it does not survive daily wear.
Why do the fine pieces all come from Russia?
Because the alkaline massifs of Kola are the largest and best worked in the world for this kind of mineral, and ornamental stone has been cut there for decades.
Tools for this stone
Astrophyllite: only the tools this stone actually concerns, each carrying the value read on this page.