Gem library
Fuchsite
The chromium mica that makes aventurine sparkle
Fuchsite is a muscovite turned green because chromium slipped into its structure. It is fuchsite, in flakes, that gives green aventurine its glitter: the two best-selling stones of the family are therefore the same thing, scattered or in mass.
- Hardness (Mohs)
- 2 – 3
- Density
- 2.78 – 2.88
- Crystal system
- Monoclinic
- Refractive index
- 1.552 – 1.618
- Cleavage
- Perfect on {001}
Mineralogical identity
- Family
- Silicates, phyllosilicates, mica group
- Species
- Muscovite
- Variety
- Chromian muscovite
- Chemical formula
- KAl₂(AlSi₃O₁₀)(OH)₂ + Cr
- Crystal system
- Monoclinic
- Classification
- Collector's mineral · ornamental stone
- Rarity
- Common
- Indicative price
- €0.10 – 3/ct
Etymology
Dedicated in 1842 to the Bavarian mineralogist Johann Nepomuk von Fuchs, who worked on silicates and on soluble glass.
Physical & optical properties
- Hardness (Mohs)
- 2 – 3
- Density
- 2.78 – 2.88
- Refractive index
- 1.552 – 1.618
- Birefringence
- 0.036 – 0.049
- Cleavage
- Perfect on {001}, into sheets
- Fracture
- Splintery
- Lustre
- Pearly to micaceous
- Diaphaneity
- Translucent
- UV fluorescence
- None
- Pleochroism
- Weak
- Colours
- green, emerald green, pale green
Formation, geology & history
A mica that swallowed chromium
Ordinary muscovite is a colourless to silver-grey mica, the commonest of the white micas. When a small fraction of the aluminium in its structure is replaced by trivalent chromium, it turns green: that is fuchsite. The chromium content stays low, of the order of a few percent, but that ion is a colorant of remarkable power, the same one that makes the green of emerald and the red of ruby. Fuchsite forms in metamorphic schists where chromium-rich ultrabasic rocks have been reworked: to find fuchsite in a terrain is to find the trace of former mantle rocks.
Fuchsite and aventurine, one story
Green aventurine is a quartzite, that is, a rock of welded quartz grains, through which flakes of fuchsite are scattered. Those flakes, oriented in roughly the same plane, reflect light together and produce the glitter called aventurescence. Aventurine is therefore quartz plus fuchsite, and fuchsite alone is the same material in compact mass. In the Brazilian deposits the two occur side by side, and a single block can pass from one to the other. Fuchsite also often accompanies ruby in Indian and Tanzanian deposits: slabs of «ruby in fuchsite», bright green flecked with red, are a shop classic.
What can be done with it, and what cannot
At hardness 2 to 3, fuchsite is one of the softest stones in the trade: a fingernail scratches it, a knock of the nail detaches scales. It is not faceted, not set in rings, and polished plates must be handled with care. Its interest is decorative and mineralogical: the colour is frank, the shimmer of the sheets is beautiful, and the natural associations with ruby or kyanite make remarkable cabinet pieces. Beads sold as «fuchsite» are almost always resin-impregnated to hold together, which should be declared.
How to recognise it
- Scales under the fingernailA fingernail is enough to detach bright flakes. No aventurine, no green quartz behaves this way: it is the one-second test.
- Shimmer by sheetsIn grazing light the surface lights up in successive patches, each corresponding to one sheet. Aventurine, by contrast, glitters in scattered points.
- Lightness and softnessDensity 2.8, but above all a greasy, almost soapy feel, very different from quartz, which is crisp and cold.
Imitations, treatments & confusions
- Aventurine sold as fuchsiteThis is not fraud, it is an approximation: aventurine contains fuchsite. But it is hardness 7 and holds up in jewellery, which fuchsite does not, and the price should follow.
- Mica dyed greenOrdinary muscovite, dyed. The dye shows between the sheets, where it accumulates, and cotton with acetone makes it bleed.
- Resin-impregnated platesVery widespread. Legitimate if declared. Too glossy a surface and a bead of water that sits instead of soaking in are the clues.
Deposits & origins
Brazil (Minas Gerais, associated with quartz to make aventurine), India (Karnataka, Andhra Pradesh), Russia (Urals), Austria, Zimbabwe, United States
Care & precautions
- Never water: it works between the sheets and breaks the stone up.
- A soft dry brush, following the direction of the sheets.
- No ultrasonics, ever: the piece disintegrates in seconds.
- Store flat, isolated, in a soft cloth. Everything scratches it.
Traditions & crystal healing
- Chakras
- Heart
- Zodiac signs
- Taurus · Aquarius
- Element
- Earth
It is sometimes called the healer's stone, and presented as a stone of recentring for those who help others. The link with the green of the heart is systematic in the handbooks. 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
Fuchsite and aventurine, the same stone?
Nearly. Aventurine is a quartzite containing flakes of fuchsite; fuchsite is the mica itself, in mass. One is hard and can be worn, the other cannot.
Can fuchsite be worn?
As a pendant, and without knocking it, yes. At hardness 2.5 that is the lower limit of wearable, and a ring would wear away in a few weeks.
Is the green natural?
In authentic fuchsite, yes, it comes from chromium. But many green micas in the trade are dyed, and the dye shows between the sheets.
Tools for this stone
Fuchsite: only the tools this stone actually concerns, each carrying the value read on this page.