Ruby Zoisite Properties, Facts and Photos
What is Ruby Zoisite?
Ruby zoisite is a metamorphic rock composed of red corundum crystals embedded in green zoisite. Black inclusions of pargasite or tschermakite, both members of the hornblende group, are often present.
Due to its striking appearance, ruby zoisite is widely used for decorative purposes. However, the difference in hardness between the corundum and zoisite can make working with it difficult.
On the Mohs scale of hardness, zoisite grades 6.5 while corundum grades 9. Diamond, the hardest mineral on Earth, grades 10 on the Mohs scale.
Gem-grade red corundum is called ruby, while all other colours are known as sapphire.
Most ruby zoisite comes from Merelani Hills in northern Tanzania. The largest deposit is the Mundarara mine, but smaller mines are operated by the Masai.
The name 'anyolite', which is also sometimes used, comes from the Maasai word 'anyoli' meaning 'green'. The Maasai prefer to call ruby zoisite 'ruby in zoisite' as an expression of pride that ruby is found on their land.
Ruby zoisite is believed to have formed during the Neoproterozoic era, which spans from approximately 1 billion to 541 million years ago.
Although often described as a mineral, ruby zoisite is a rock because it's composed of two different minerals, corundum and zoisite. Ruby zoisite is often mistaken for ruby in fuchsite, which can look very similar. Most ruby in fuchsite comes from southern India, and because it's not as rare, is considerably cheaper.
Fuchsite, a type of green mica, is much softer than zoisite.
Longido Ruby - The Red Corundum in Ruby Zoisite
Longido ruby was discovered in Longido, northern Tanzania, in 1949 by prospector Tom Blevins.
Having stumbled across an outcrop of weathered green rock, with closer inspection, he found well-formed ruby crystals partially exposed, their distinctive red colour standing out sharply against the green matrix of the host rock.
Significant amounts of Longido ruby were initially found near the surface. However, over time, mining efforts moved underground and extensive operations are now required to extract the stones.
Most Longido ruby is found within a matrix of green zoisite and amphibole rock. This material is commonly known as ruby zoisite or ruby in zoisite.
The name 'ruby in zoisite' is widely used around the world and happens to be a more accurate description of what this stone is.
Although translucent facet-grade rubies have been discovered, they're incredibly rare.
Longido is located in the Arusha region of northern Tanzania, near the border with Kenya. The city of Arusha is often used as a base for those who climb Mount Kilimanjaro. It's also part of a broader gemstone-rich area, which includes the Merelani Hills, where tanzanite is found.
Article Pictures
The ruby zoisite in the picture at the top of our article is displayed in the Smithsonian Museum of Natural History, Washington D.C. Photo by Stone Mania.
The second and third pictures are courtesy of Stan Celestian. Both are clickable and redirect to the original image.
Pop-up photos: Ruby zoisite - Courtesy of Géry Parent. The ruby in Fuchsite stones is a licensed image.
