Short answer: ruby zoisite, also sold as anyolite, is a metamorphic rock from Tanzania: grass-green zoisite holding opaque, pink-red ruby crystals and often black specks of the amphibole tschermakite. It is carved into spheres, towers, tumbles and cabochons, not faceted. Hardness runs from about 6 in the zoisite to 9 in the ruby, and the ruby patches usually glow red under UV. The look-alike to rule out is ruby in fuchsite, which is far softer.
What is ruby zoisite made of?
It is a rock with three main ingredients, which is why its properties change from spot to spot on the same piece. Geology.com defines anyolite as a very colorful rock composed mainly of zoisite, with bright red ruby crystals, sometimes accompanied by black crystals of the hornblende tschermakite.
| Component | Chemistry | Mohs hardness | Specific gravity |
|---|---|---|---|
| Zoisite (green matrix) | Ca2Al3(SiO4)(Si2O7)O(OH) | 6 to 6.5 | 3.2 to 3.4 |
| Ruby (red crystals) | Al2O3, colored by chromium | 9 | 4.01 |
| Tschermakite (black specks) | Calcic amphibole | not a major factor | not a major factor |
The zoisite figures come from Minerals.net, which gives a hardness of 6 to 6.5 and specific gravity 3.2 to 3.4 in the orthorhombic system; Webmineral gives a calculated specific gravity of 3.30. For the ruby, Webmineral's corundum data lists hardness 9 and specific gravity 4.01. Combined, a ruby zoisite sphere feels noticeably heavy for its size compared with a quartz sphere at 2.65.
Webmineral also notes the mineral's name honors Siegmund Zois (1747 to 1819), an Austrian natural scientist, and that zoisite itself is non-fluorescent. The same species gives the trade two better-known varieties: blue tanzanite and pink thulite. Ruby zoisite is the opaque, green, everyday member of that family.
Where does ruby zoisite come from?
Tanzania. Minerals.net describes Tanzania as the producer of massive green zoisite with opaque ruby at Longido, near Mount Kilimanjaro, and lists "Ruby Zoisite" as a mixture of opaque red ruby in a green zoisite matrix from Tanzania. Longido is in the Arusha Region of northern Tanzania, the same region that hosts the Merelani Hills tanzanite field that Webmineral names as the locality for its gem tanzanite crystal.
The ruby in Longido rock is not gem ruby. It forms as rounded to hexagonal crystals, usually opaque, pink-red to purplish, often with pale rims or internal fractures. That is why ruby zoisite is sold by size and pattern rather than by carat.
How does ruby zoisite form?
Zoisite is a metamorphic mineral. Geology.com explains that zoisite and clinozoisite form during the regional metamorphism and hydrothermal alteration of igneous, metamorphic and sedimentary rocks, appearing as massive material and as prismatic crystals in veins cutting schists and marbles. Ruby zoisite records rock that was buried and recrystallized at high temperature and pressure: aluminum-rich, silica-poor parts grew corundum, chromium tinted that corundum red and the surrounding calcium-aluminum silicate green, and amphibole crystallized alongside. The metamorphic minerals guide covers that process across other species.
Why does ruby zoisite glow under UV light?
The ruby does the work. GIA explains that chromium is the trace element that causes ruby's red, and that chromium can also cause fluorescence. Webmineral's corundum entry records that corundum is sometimes fluorescent, with longwave UV giving red. The zoisite matrix does not respond, so under a longwave lamp in the dark, a good ruby zoisite piece shows glowing red-pink patches against a dark green to black background.
GIA also notes that iron can mask ruby's red fluorescence, which is why some ruby patches glow strongly and others hardly at all. Glow strength is a nice bonus, not a test of authenticity. For more on the general physics, see the fluorescence guide.
How do you tell ruby zoisite from ruby in fuchsite and ruby in kyanite?
Three ruby-bearing rocks share shelf space and are often confused. Geology.com is direct on the main mix-up: ruby in fuchsite is often misidentified as ruby in zoisite, and the two separate easily on hardness, because green fuchsite has a hardness of only 2 to 3 while green zoisite has a hardness of at least 6. Geology.com adds that most ruby in fuchsite shows blue kyanite alteration rims around the ruby crystals, which do not occur around rubies in zoisite.
| Feature | Ruby zoisite | Ruby in fuchsite | Ruby in kyanite |
|---|---|---|---|
| Green or blue matrix | Grass to olive green zoisite | Emerald-green, micaceous fuchsite | Blue to gray-blue kyanite |
| Matrix hardness | 6 to 6.5 | 2 to 3 | Varies by direction |
| Matrix luster | Waxy to vitreous, even | Pearly, sparkly mica sheen | Vitreous to pearly, bladed |
| Rims on ruby | None | Often blue kyanite rims | Ruby sits directly in kyanite |
| Black specks | Tschermakite common | Less typical | Less typical |
Checks a buyer can do without damaging anything:
- Look at the green under a loupe. Fuchsite shows flaky, glittering mica; zoisite looks solid and waxy.
- Look around the ruby. A thin blue halo between ruby and green points to ruby in fuchsite.
- Feel the polish. Fuchsite takes a softer, slightly greasy polish and scuffs easily; zoisite holds a crisper shine.
- Read the listing. Origin Tanzania and the word zoisite or anyolite belong together; a listing that names fuchsite or kyanite is a different rock, whatever the photo suggests.
The kyanite guide covers the blue matrix stone, and the planned fuchsite guide covers the mica one. If the question is whether the red crystals are ruby at all rather than garnet, see the garnet vs ruby comparison.
Is ruby zoisite treated or imitated?
Most ruby zoisite is sold as mined and polished. Watch for dyed material where the red is too uniform or bleeds into cracks, and for resin-filled or stabilized blocks, which feel warmer and lighter and show a plastic-like surface at fractures. Reconstituted "ruby zoisite" made of crushed stone in resin shows angular fragments in a binder under magnification. The broader picture is in the guide to stabilized and reconstituted stones.
How should you care for ruby zoisite?
The hardness mismatch is the main issue. Ruby at 9 and zoisite at 6 to 6.5 polish at different rates, so the ruby crystals often stand slightly proud of the surface or show small pits where they meet the matrix. Zoisite has one perfect cleavage, so carvings and thin towers can chip at edges if knocked.
- Clean with lukewarm soapy water and a soft brush, then dry.
- Avoid ultrasonic cleaners on pieces with visible fractures.
- Store spheres on a stand or soft ring so they do not roll into harder stones.
- Sunlight does not fade it; the colors are stable for display.
What is ruby zoisite associated with in crystal traditions?
In crystal traditions, ruby zoisite is associated with joining passion and patience, a reading drawn from its red-in-green appearance, and with the heart chakra. It is a common choice for palm stones and spheres in that context.
Choosing a ruby zoisite piece
Look for strong contrast: deep green zoisite, ruby crystals with real red rather than gray-pink, and black tschermakite as accent rather than as dominant mass. In spheres, check that rubies are scattered across the whole surface and that the polish runs smoothly over the ruby-zoisite boundaries without deep pits. Ask the seller to name the matrix, because a listing titled only "ruby" can mean any of the three rocks.
- Ruby Zoisite: large tumbles of Tanzanian-type ruby zoisite, an inexpensive way to compare the green zoisite, red ruby and black specks in hand. The listing notes the ruby reacts under a black light.
- Ruby Zoisite Sphere: a polished sphere of about 36.5 mm. A sphere shows ruby distribution on every side, which makes it the best format for judging pattern quality.
- Ruby in Fuchsite Tumbles: the most common look-alike, worth owning for comparison. Look for the mica sparkle and blue rims described above.
- Ruby in Kyanite: spheres around 47 to 49 mm and freeforms in blue kyanite, the third ruby rock in the family.
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Ruby zoisite and ruby rocks in stock
Frequently asked questions
Is ruby zoisite real ruby?
Yes. The red crystals are corundum colored by chromium, which is ruby by definition. They are opaque, fractured and not faceting grade, so ruby zoisite is valued as an ornamental rock rather than as gem ruby.
What is the difference between anyolite and ruby zoisite?
None. Anyolite is another name for the same rock, green zoisite with ruby crystals and often black tschermakite. Minerals.net lists anyolite as a synonym of ruby zoisite, and Geology.com uses the two names interchangeably.
Does ruby zoisite glow under black light?
Often, yes. The chromium in ruby can fluoresce red under longwave UV, so the ruby patches light up while the green zoisite stays dark. Rubies with more iron glow weakly or not at all, so a dull response does not mean a fake.
How can I tell ruby zoisite from ruby in fuchsite?
Check the green. Fuchsite is a mica with a hardness of 2 to 3 and a sparkly, flaky look, and its rubies often have blue kyanite rims. Zoisite is 6 or harder, looks solid and waxy, and its rubies sit directly in the green.
Where is ruby zoisite mined?
The source named for the trade material is Longido, near Mount Kilimanjaro in northern Tanzania. The same country produces tanzanite, the blue variety of zoisite, from the Merelani Hills in the Arusha Region.
Sources
- Geology.com, Zoisite and Clinozoisite: https://geology.com/minerals/zoisite.shtml
- Minerals.net, Zoisite: https://www.minerals.net/mineral/zoisite.aspx
- Minerals.net, Anyolite: https://www.minerals.net/gemstone/anyolite_gemstone.aspx
- Webmineral, Zoisite mineral data: https://webmineral.com/data/Zoisite.shtml
- Webmineral, Corundum mineral data: https://webmineral.com/data/Corundum.shtml
- GIA, Ruby: https://www.gia.edu/ruby-description