Short answer: fuchsite is muscovite mica in which some aluminum has been replaced by chromium, which turns it a glittering emerald to grass green. It is very soft (about 2 to 3 on the Mohs scale), splits into thin flexible sheets, and grows mostly in low-grade metamorphic rock. Collectors meet it as raw green mica, as "ruby in fuchsite" with red corundum, and as the green flakes inside green aventurine.
What is fuchsite, exactly?
Fuchsite is not a separate mineral species. It is a chromium-bearing variety of muscovite, the most common member of the mica group. Geology.com explains that in muscovite, aluminum is sometimes replaced by magnesium, iron, lithium, chromium or vanadium, and that when chromium substitutes for aluminum the mineral takes on a green color and is known as fuchsite. Webmineral lists "Fuchsite (Cr)" as a synonym under muscovite rather than as its own entry.
| Property | Fuchsite (chromian muscovite) |
|---|---|
| Formula | K(Al,Cr)2(Si3Al)O10(OH)2 |
| Crystal system | Monoclinic |
| Mohs hardness | about 2 to 2.5 on the sheet face |
| Specific gravity | about 2.8 (muscovite 2.77 to 2.88) |
| Cleavage | One perfect direction, {001} |
| Tenacity | Sectile; thin sheets are elastic |
| Luster | Pearly to vitreous |
The mica structure explains almost everything about how fuchsite behaves. Muscovite is built from stacked sheets of linked silicon-oxygen tetrahedra, held together by a layer of potassium. The bonds within a sheet are strong; the potassium layer between sheets is weak. That is why a fuchsite flake peels into thinner and thinner leaves with a fingernail, why each leaf bends and springs back instead of snapping, and why the broad faces flash light like tiny mirrors. Minerals.net describes muscovite's tenacity as sectile and elastic, and Geology.com notes that its perfect cleavage lets it split into thin, flexible, elastic sheets, which it calls unique among common minerals.
Why is it green?
Chromium. The Caltech Mineral Spectroscopy server notes that micas usually owe their color to iron, manganese, titanium and chromium, and that chromium in the 3+ oxidation state contributes an intense green to some micas. Its reference green muscovite, from near Randsburg in Kern County, California, shows the typical Cr3+ absorption near 600 nm. Absorbing orange-red light near 600 nm is what leaves the eye seeing green, the same element at work in emerald and ruby.
The more chromium, the deeper the color. Pale fuchsite can look sage green; chromium-rich flakes look almost emerald.
Where and how does fuchsite form?
Chromium is rare in most crustal rocks but common in ultramafic rocks such as serpentinite and peridotite, the mantle-derived rocks described in the peridot guide. When fluids moving through those rocks meet aluminum-bearing rock during metamorphism, chromium can end up in the new mica that grows. Geology.com notes that fuchsite is often found disseminated through metamorphic rocks of the greenschist facies, the lower-temperature end of regional metamorphism. The metamorphic minerals guide explains what those facies mean.
Where fuchsite is abundant enough to color a whole rock green, Geology.com notes that the rock is called verdite. Verdite is carved as an ornamental stone, and it is one reason a solid green "fuchsite" carving is often a fuchsite-rich rock rather than a block of mica.
What is mariposite?
California has its own green mica rock with a local name. Minerals.net describes mariposite as a green form of muscovite in small, dense flake groups from Mariposa and Tuolumne counties, forming in metamorphosed dolomite and quartz, usually as veins or as a base material. The green mica with its quartz and carbonate host makes a rock that is also called mariposite and is used as an ornamental stone. Those counties sit on California's Mother Lode gold belt, and the green rock is a familiar sight in that country.
What is ruby in fuchsite?
Ruby in fuchsite is a metamorphic rock in which red to pink corundum crystals sit in a matrix of green fuchsite, often with blue kyanite. Corundum colored by chromium is ruby; Geology.com's corundum page notes that chromium produces the red of ruby and that corundum is the index mineral for hardness 9. The same chromium that colors the mica colors the rubies, which is why the two grow together.
Most ruby in fuchsite rubies are opaque, fractured and pinkish, nowhere near gem quality. The material is valued as a decorative stone: spheres, eggs, tumbles and slabs where the contrast between red and green carries the piece.
Why do the rubies have blue rims?
Look closely at the edge of each ruby. According to Geology.com's zoisite page, most specimens of ruby in fuchsite show blue kyanite alteration rims around the ruby crystals, and this does not occur around rubies in zoisite. The blue halo is a reaction zone, kyanite growing where the corundum and its surroundings reacted during metamorphism. For the mineral itself see the kyanite guide.
Ruby in fuchsite or ruby in zoisite?
These two red-and-green rocks are confused constantly. Geology.com says ruby in fuchsite is often misidentified as ruby in zoisite, and that careful testing separates them easily because green fuchsite has a hardness of only 2 to 3 while green zoisite is at least 6.
| Check | Ruby in fuchsite | Ruby in zoisite (anyolite) |
|---|---|---|
| Green matrix | Fuchsite mica, glittery and flaky | Zoisite, dense and grassy green |
| Hardness of the green | 2 to 3 | At least 6 |
| Blue rims on rubies | Usually present (kyanite) | Absent |
| Black accents | Uncommon | Often black hornblende |
| Polish | Green areas dull and undercut | Even, glassy polish |
The polish row is the easiest at-home tell. On a polished sphere of ruby in fuchsite the hard rubies stand slightly proud of the soft mica, and under a light you can see the fuchsite areas are softer and less glossy. More on the zoisite rock in the ruby zoisite guide.
The rubies in both rocks often glow under ultraviolet light. GIA notes that chromium can cause fluorescence and that low-iron rubies typically fluoresce red under ultraviolet light. A longwave lamp is a quick, fun test; a strong red glow from the red crystals is consistent with ruby, though iron-rich rubies may glow weakly or not at all.
How does fuchsite relate to green aventurine?
Green aventurine is quartz rock with fuchsite flakes inside it, a topic the aventurine guide covers. The angle that matters here is what happens to a polished stone. Geology.com's aventurine page notes that just a few percent fuchsite by volume gives a distinct green, that some aventurine carries ten to twenty percent, and that coarse grains form pits wherever they meet the polished surface. A pitted, slightly dimpled green palm stone is a sign of coarse fuchsite plucking out of the quartz during polishing. For a side by side, see fuchsite vs aventurine.
How do you identify fuchsite?
- Fingernail test on a hidden spot. Webmineral puts muscovite at 2 to 2.5, between gypsum and a fingernail; pure fuchsite can be marked by a fingernail edge. Quartz-based stones cannot.
- Peel test on rough. A flake lifts off along the cleavage and bends without breaking.
- Glitter that comes from the stone, not inclusions. In pure fuchsite the whole surface sparkles in layers; in aventurine isolated flakes sparkle inside glassy quartz.
- Weight. At about 2.8, fuchsite feels similar to quartz, so weight separates it from heavy look-alikes such as malachite but not from aventurine.
How do you care for fuchsite?
Handle raw fuchsite as you would any mica: it sheds glittering flakes onto hands and shelves. Keep it out of tumble bags with harder stones and away from abrasive cleaning. A dry soft brush is the best cleaner; mica does not dissolve in water, but soaking loosens layers and flakes. For ruby in fuchsite, wipe with a barely damp cloth and dry it, and store spheres on a soft stand, since the mica areas scratch easily.
Fuchsite in crystal traditions
In crystal traditions fuchsite is associated with renewal and lightheartedness, and ruby in fuchsite with balancing passion and patience. These are cultural associations, not mineral properties.
Buying fuchsite: what to look for
Decide which fuchsite you want. Raw fuchsite should show bright, saturated green with visible layering and fresh, unbroken sheets. Ruby in fuchsite is judged on the number, color and spacing of the rubies and on the contrast with the green, with blue kyanite rims as a mark of the real thing. Expect polished ruby in fuchsite to have a softer luster on the green areas; a uniformly glassy surface suggests zoisite or a coating.
Examples currently in stock:
- Fuchsite rough: unpolished green mica pieces, the best way to see the peel, sparkle and softness described above.
- Ruby in fuchsite tumbles: medium tumbles that show the red and green contrast up close; check under a longwave lamp for the ruby glow.
- Ruby in fuchsite spheres and display piece: a 47.5 mm sphere and a 150 mm, 21.5 lb display piece, where the softer mica areas and harder rubies are easy to compare.
- Ruby zoisite tumbles: the rock most often confused with ruby in fuchsite; set them side by side and look for the missing blue rims.
- Ruby in kyanite: spheres and freeforms where the blue mineral that rims the rubies in fuchsite is the main matrix.
- Green aventurine: tumbles, palm stones and tall towers of quartz colored by fuchsite flakes, the most common way people already own fuchsite.
Digital Towns Market
Fuchsite in stock
Frequently asked questions
Is fuchsite the same as green mica?
Fuchsite is one kind of green mica: muscovite with chromium in place of some aluminum. Other micas and mica-like minerals can be green from iron, so "green mica" is broader. The bright, emerald to grass green flakes sold as fuchsite owe that color to chromium.
Why is fuchsite so soft and flaky?
It is a mica. Its atoms form strong sheets held together by weak potassium layers, so it splits easily into thin leaves and scratches at about 2 to 2.5 on the Mohs scale. The same structure makes thin flakes flexible and elastic, which is why fuchsite sheds glitter onto your hands.
How can I tell ruby in fuchsite from ruby in zoisite?
Check the green and the rims. Fuchsite is glittery and soft, about 2 to 3, while zoisite is dense and at least 6. Most ruby in fuchsite also shows blue kyanite rims around the rubies, which ruby in zoisite lacks. Zoisite often carries black hornblende specks instead.
Do the rubies in ruby in fuchsite glow under UV?
Often, yes. Chromium causes ruby's red fluorescence, so many of the red crystals glow under a longwave ultraviolet lamp. Rubies with more iron glow weakly or not at all, so a dull response does not mean the stone is fake.
Can fuchsite get wet?
Mica does not dissolve, so a brief wipe or rinse will not harm it. Soaking is the problem: water works between the layers and lifts flakes, and it can loosen the mica around rubies. A soft dry brush is the safer routine for raw pieces and polished ruby in fuchsite.
Sources
- Geology.com, Muscovite: https://geology.com/minerals/muscovite.shtml
- Webmineral, Muscovite Mineral Data: https://www.webmineral.com/data/Muscovite.shtml
- Minerals.net, Muscovite: https://www.minerals.net/mineral/muscovite.aspx
- Caltech Mineral Spectroscopy Server, Mica spectra: http://minerals.gps.caltech.edu/files/visible/mica/index.html
- Geology.com, Corundum: https://geology.com/minerals/corundum.shtml
- Geology.com, Zoisite and Clinozoisite: https://geology.com/minerals/zoisite.shtml
- GIA, Ruby Description: https://www.gia.edu/ruby-description
- Geology.com, Aventurine: https://geology.com/gemstones/aventurine/