Gem Profile May 20: Ruby Zoisite

By on May 19, 2011
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Daily Wire Jewelry Making Tip for
May 20, 2011

Ruby Zoisite

Cathy Whitten's Ruby Zoisite Necklace

A Closeup of Cathy Whitten's Ruby Zoisite Necklace

This week’s featured gem or rock is Ruby Zoisite. We chose this interesting stone after seeing the lovely necklace made by Cathy Whitten, our Wire Jewelry Artist of the Month. You can see pictures and read all about Cathy and her ruby zoisite necklace at our Featured Wire Artist of the Month: May 2011 page.

While deciding how to begin this article, the Shakespearean quotation, “A rose by any other name would smell as sweet” came to mind more than once; what matters is what something is, not what it is called. So let me explain some terminology briefly. As a rockhound who continuously studies mineralogy and geology, it is sometimes difficult for me to term something which I would call a “rock” as a gemstone. A “rock” is a combination of two or more minerals, and a “gemstone” is what the jewelry industry calls a specific mineral. There are also many “rocks” that have been accepted as gems due to their unique appearance. Some individuals call these rocks by the unscientific label “semi-precious”; I just call them “gem-rocks.” (“Semi-precious” refers to all stones excluding the traditional “precious” stones: diamond, ruby, sapphire, and emerald).

A very colorful material, ruby zoisite is a metamorphic gem-rock composed of at least three minerals:

Epidote Crystal Fan

Dark green Epidote Crystal Fan specimen from Peru. -Dale Armstrong, private collection.

corundum, epidote and tschermakite (more commonly known as hornblende). The various shades of apple green is chromiferous zoisite; the black and very dark green spots and striations are edenitic hornblende; and the lovely reddish pink is corundum (ruby). The geological name for African ruby-in-zoisite is Anyolite, from the Maasai native word for green.



Carved Ruby Zoisite Flowers

Flowers carved of Ruby Zoisite from Longico Mine, Tanzania, Africa. Notice the crystal structure on the bottom left flower (upside-down). -Dale Armstrong, private collection.

Ruby Zoisite was first discovered in Austria in 1805 and was named for Baron Sigmund Zois, the naturalist who identified the mineral composition as a new find in the mineralogy world. The better known east Africa deposits were first documented in 1904 by a German military commander and scholar who collected the material named after himself, “Merkerstein.” His work was never published and the location was lost. Around 1949, these “ruby-in-zoisite” deposits were rediscovered in Tanzania, mistakenly thought to be valuable for the ruby. With all three components being extremely dense metamorphic rocks, early miners found it impossible to profitably separate the ruby from the zoisite.

Although a very few gem quality rubies have been found, unshattered by its matrix, African Ruby Zoisite has gained popularity in the jewelry making industry, also known as Tanganyika Artstone. The majority of what we see on the market today comes from the Longido mine located at the foot of Mt. Kilimanjaro in Tanzania, Africa. Very plentiful, this ruby zoisite has a combined Mohs hardness of 5 to 7 and most of it takes a good polish.

Ruby Zoisite Pendant by Teresa McMahon

Ruby Zoisite Pendant by Teresa McMahon

The mineral Zoisite occurs in a variety of colors that include green, brown, pink, yellow, gray, colorless and shades of blue to violet. When natural zoisite is found in its reddish brown crystal state and it is artificially heated to bring out the violet and blues, it is named Tanzanite, rather than being called blue-zoisite. (We will talk more about Tanzanite at a later date.) Zoisite formations can be found in a variety of places around the globe including, but not limited to: Africa, Austria, India, Pakistan, Switzerland and the United States.



Rubies and Sapphires encased in Smaragdite

Rubies and Sapphires encased in Smaragdite from Mitchell Co, NC. -Dale Armstrong, private collection

Ruby zoisite is not a rare material, so there is no need to try to imitate it. However, we do need to be aware of two other gem-rocks that look similar and are often mislabeled. One similar gem-rock is from Mitchell County, North Carolina that is actually an emerald green form of actinolite, named smaragdite, with corundum, both red/pink and blue. Smaragdite can be difficult to polish because of the difference in the mineral hardness. The other material that is often mistaken for ruby zoisite is the subject of next week’s Gemstone Profile, yet another gem-rock called Ruby Fuchsite, when I will show you comparison photos of all three materials.



Book Resources:

  • Rocks, Gems, and Mineral Collecting Sites in Western North Carolina by Rick Jacquot Jr,
    ISBN-10: 1566642485, ISBN-13: 978-1566642484
  • Rubies & Sapphires (Fourth Edition) by Fred Ward, ISBN-10: 9781887651103, ISBN-13: 978-1887651103
  • Peterson Field Guide – Rocks and Minerals by Frederick H. Pough, ISBN-0-395-91096-X

Internet Resources:

Gem Profile by Dale “Cougar” Armstrong

Next Friday’s Gem Profile is on Ruby Fuchsite. Have you wire wrapped Ruby Fuchsite before? Send us pictures at and they could be featured!

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  1. avatar

    Frankie Harvener

    May 20, 2011 at 8:11 am

    Thanks for adding this very excellent informational section to your newsletter. I enjoy your tips and also the tutorials and instruction. I recently purchased a lovely pendant of ruby zoisite with matching earrings from a shop in Ohio. Have enjoyed wearing them. I am tempted to start another stone collection to go with my many other stones in “stash”! :-)

  2. avatar


    May 20, 2011 at 9:58 am

    Love ruby zoisite. Between Dale and my husband (who we refer to as a rock “snob”) I manage to get a great insight into all the various gem rocks we find and collect. Neither of them consider my questions dumb and we have had some really good sessions sitting out on the patio about gem stone.

    Dale is well aware of how much I love ruby zoisite and always look for it at shows. Thanks to her I know my gem rocks more in depth and know what to look for at shows when it comes to quality and price.

    Once again, Dale has shown the depth of her personal knowledge and experience by presenting this gem rock and explaining to us. Thanks Cougar….

  3. avatar

    Heidi Rousseau

    May 20, 2011 at 12:29 pm

    Wonderful article!!!I just learned a lot about minerals,rocks and semi precious stones. Thank you

  4. avatar

    Barbara Wolf

    May 20, 2011 at 4:22 pm

    Very beautiful Artical,love Ruby Zoisite. Love the Flower Pieces you have, outstanding.look forward to more Gem stone write ups, thank you Dale.

    • avatar


      May 20, 2011 at 9:50 pm

      Thanks Barbara, being able to write about stones is a refreshing break for me.

  5. avatar

    Marcia Fruland

    May 21, 2011 at 1:21 pm

    Hi Dale,
    Thank you so much for all the tips! I really enjoy the “rock” articles, very interesting and informative! I look forward to the next one.

  6. avatar

    Lori Crawford

    May 21, 2011 at 5:24 pm

    Thank you so much for adding the stone clarification mailings! I have so much enjoyed learning more about the different types of stones. It makes it a lot easier when making a piece of jewelry if you know exactly what kind of stone you are making it with and where it came from. Again thank you! It is a welcome addition to everything else you so for us jewelry designers!