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                           Mineral of the Month--May

                              Tsavorite

                                      Calcium Aluminum Silicate

                                      Ca3Al2SiO4

 

                   Tsavorite

               By Karissa Hendershot

Preface
Introduction
Tsavorite article
Members' Gallery
Article Contributors
Photo & Graphics Credits
Invitation to Members
Past Minerals of the Month
tsavorite_display.jpg (8290 bytes) 3140tn.jpg (35626 bytes)
 

With a gemmy green that rivals emerald...

 

 

...this grossular beauty can astound us!


(Top, left): Tsavorite gems.  Photo courtesy of wikipedia.org   2006

(Top, right): Columbian Emerald.  Photo by and courtesy of IC Minerals   2006

Preface    

    Welcome to another guest author's article!  This month, we are visiting Tsavorite, a newly
popular gemstone.  Enjoy!

 

Introduction

     In this month's installment, we will pay a brief visit to a bright green favorite: Tsavorite.
A gemmy garnet by nature, when faceted, this stone is adorning modern jewelry the world over.

     Our guest author, Karissa Hendershot, is DMS's current President.  Although her first love
is for fossils, her knowledge of and experience with minerals has grown over the years.   Please
join us for a long-awaited look into garnets.

 

Tsavorite

 

image002.jpg (4835 bytes) This exceptional 7.24 ct. Tsavorite cushion was mined from the Bridges' Scorpion mine and is now on loan to The Smithsonian Museum in Washington, D.C

 

Campbell and Judith Bridges, Tsavorite USA, Inc.

 

Properties of Tsavorite Garnet

 

image004.jpg (3185 bytes)

 

Tsavorites are not an acknowledged mineral species.  Instead Tsavorite is a variety of Grossular garnet.

Tsavorite, the trade name for green grossular garnet, was named by Tiffany & Co after the location, where it was first discovered by the Geologist Campbell Bridges in 1968.

 

Photo by ICA Gem Bureau Idar-Oberstein

CHARACTERISTICS OF TSAVORITES

Composition                  Ca3Al2(SiO4)3

Hardness (Mohs)           7-7.5

Specific Gravity  3.60–3.68

Refractive Index 1.740; Singly refractive

Crystal System  Cubic

Colors                           Light to Deep Green

Pleochroism                  None

Dispersion                     0.028

Phenomena                   NONE

Enhancements  Generally None

Synthetics                     None

Handling:                       Ultrasonic: generally safe, but risky if the gem contains liquid inclusions. Steamers: not safe. The best way to care for Tsavorite garnet is to clean it with warm, soapy water. Avoid exposing it to heat or acids.

Sources. The original locality for Tsavorite was Kenya’s Tsavo National Park, but today important deposits of gem tsavorite have also been found in Tanzania’s Lindi Province.

Why is it called Tzavorite or Tzavolith respectively if it is after all a green Grossularite from the colorful Garnet family? Naming gemstones is performed according to certain rules. Modern mineralogical nomenclature demands that gemstones are given a name ending in "ite". To honour the Tzavo National Game Park and the Tzavo river running through this area, Henry Platt , the former president of Tiffany & Co, who accompanied the gemstones rise to popularity, had suggested the name Tzavorite. Sometimes, however, Tzavolith is used but both denote the same stone. The ending "lith” is simply the Greek word for "stone”. Additionally, the “z” is often replaced with an “s” changing the spelling from Tzavorite to Tsavorite. Both version seem to be perfectly acceptable spellings for the gem stone as well as the area the garnet was named after.

Tsavorite

HISTORY

 

"Everyone knows about precious diamonds, rubies or emeralds. But only the real experts know about tsavorite. Tsavorite is also called green grossular garnet. It is a rare gemstone mined in the Kenyan part of the Mozambique belt which is in the bushland along the frontier between Kenya and Tanzania in the Tzavo National park.  The sparse mines there are situated in a uniquely beautiful landscape of dry grassland with bare and dry hills. It is a dangerous region, where snakes feel at home and now and then a lion will hunt for prey.

 

The Brilliant green Tsavorite is rather a young gemstone with a truly ancient geological history.  In 1967, the British geologist Campbell R. Brides was prospecting for gemstones in the north-eastern part of Tanzania. Suddenly he came across some very odd, potato-shaped stone objects. And like in a fairy tale, he found breathtakingly beautiful green grains and crystal pieces inside these weird objects. Gemological tests showed that he had discovered green grossularite, a mineral which had up to then been considered very rare, which belongs to the colorful Garnet family. The stones were very beautiful and of high transparency, so that his find made experts sit up ad take notice. Even Tiffany & Co. in New York expressed their interest in the newly discovered green jewel. But in spite of all efforts it was impossible in those days to get an export license for taking these stones out of Tanzania. Campbell Bridges, however, did not admit defeat. As geologist he knew that those layers in the soil which carry gemstones are generally not limited to just one spot, but usually stretch out over vast areas – and such a layer was what he had encountered according to his opinion. After all, the stone belt which accommodates most of East Africa’s gemstone mines is truly ancient.

 

Campbell R. Bridges stubbornly continued his search. His theory that the gemstone loaded vein might even extend into the Kenyan territory finally set him on the right track. In the year 1971 he discovered the brilliantly green gemstone for a second time, this time in Kenya, where he could officially register his find and could start exploiting the occurrence. This was the beginning of a new adventure: in order to protect himself from wild animals Bridges lived in a tree house at first. And as he did not want his treasure to be stolen, he cunningly employed the workers’ fear of snakes and had the rough stones guarded by a python snake. It was a beautiful find indeed. Unfortunately, however, the stone was only known to experts. This changed quickly when in 1974 Tiffany’s started a special promotion campaign making Tzavorite well-known in all the USA in only a short time. Other promotion campaigns in other countries followed, and soon Tzavorite was a name known everywhere.

 

GEOLOGY

 

Africa was covered by the ocean millions of years ago at a time when the continents where moving around a great deal more than they are now.  Layers of organic sediment were deposited, and compacted to form shale. The land was subjected to intense heat, pressure, folding and uplift, metamorphically changing the ocean floor into new minerals. This twisting and torturing of the rocks gave birth to the unusual gemstones of East Africa, many colored by the vanadium which is plentiful in these rocks.

 

MINING

 

Most deposits of tsavorite are found in small and unpredictable pockets.  From a mining standpoint, it is very difficult to figure where to mine next. There have been about 40-50 different areas where tsavorite has been mined. Today, only four mining ventures are still producing. The Scorpion Mine owned by Campbell Bridges is located in Mindi-Kandashi, southeast Kenya. The Aqua Mines, with 3000 acres are located in the Tsavo National Park near Kasigau,  Lualenyi Mine is located in Voi, Kenya and a new tsavorite-producing area was recently discovered in Lokirima, about a thousand kilometers northwest of the previously known localities. Hopes are high that this location will start producing rough suitable for faceting.

 

Tsavorite is often found in pods which miners call potatoes. The green color is most often due to vanadium or chromium. The early geology which formed tsavorite shattered most of the crystals. Tsavorite mining requires expensive earth removal equipment. It is very rare to find tsavorite in sizes larger than three carats. Most tsavorites are carat size or smaller. (Ed. note: The largest tsavorite we have ever bought/sold was a gem 15.41). Compare this to the wide availability of tanzanite above 10 carats.

 

MINERALOGY

 

Tsavorite has a vivid green color with a high refractive index and double the dispersion of emeralds, giving tsavorite potential greater brilliance. It has a garnet's durability and high clarity.  Tsavorite is often found in pods with a coating of quartz or scapolite, which the miners call "Potatoes". The green color is due to the vanadium from the host rock, but some tsavorite is also colored by chromium. It is very rare to find tsavorite bigger than 5 carats because the heat and pressure which formed tsavorite millions of years ago shattered most of the crystals. 85% of the mined stones are smaller than 1 carat, 10% are bigger than 1 carat, 2.5% are bigger than 2 carats, 1% is bigger than 3 carats.  Only occasionally a rough crystal of over 5 carats is found, so that cut Tzavorites are quite rare and valuable starting from sizes of 2 carats on. The brilliance and luminosity of the stone are displayed even in smaller sizes.

 

DESIRABILITY

 

What makes Tzavorite so desirable? First of all there is its vividly brilliant green. The color scale shown by Tzavorite ranges from spring-like pale green via intensely bluish green to deep forest green; colors which have an invigorating and fresh effect on the senses. The gemstone is also coveted because of its high brilliance. Like all other Garnets it enjoys an especially high light refraction index (1.734/ 44).  Compare a tsavorite with an emerald. Both gems were formed under conditions of great stress, and are seldom found in sizes large enough to cut clean stones above two carats. Tsavorite is 200x rarer than emerald, sells for about 1/4 the price, is more brilliant due to a higher refractive index (1.74 vs. 1.596 for an emerald) and is harder than an emerald. Finally, 99.9% of all emeralds are oiled or opticoned and tsavorite is not treated in any way. Tsavorites are more durable, cost less and are more brilliant than emeralds!  Sparks one’s interest doesn’t it!

image005.gif (33558 bytes)
Campbell and Judith Bridges, Tsavorite USA, Inc.

Contrary to other gemstones, Tzavorites are not heated or oiled. This is not necessary for this gemstone. Like all other Garnets it is a piece of immaculate and pure nature. Another positive characteristic is its robustness. Although showing a hardness similar to Emerald - about 7 1/2 on the Mohs Scale – it is far less sensitive in its handling. This is not only important for cutting and setting the stone, but also for wearing. Tzavorite is less likely to become damaged or to splinter even as consequence of abrupt or incautious impact. It is excellently suited for the favored style of "invisible setting", where stones are set closely joined, and which cannot be recommended for Emeralds. Due to its high brilliance, Tzavorite here is an equal match for the classical stones like Diamond, Ruby and Sapphire.

WHAT TO LOOK FOR

When collecting cut tsavorite, you need to look for an intense vibrant green color. It should be similar to imperial jade or emerald green. They should be at least one carat in size and a standard shape. You want to avoid gems that look like peridot (green/yellow) or stones that are too dark in tone (green/black). Like emeralds, tsavorite can be green/blue or green/yellow. And like emerald, different collectors have opposing secondary color preferences. There is no market preference on which color is the optimum. In AGL terms, it is practically impossible to receive a straight 3.5 color in emerald; it is similarly as difficult to receive a 3.5 tsavorite. A 4 or 4.5 color tsavorite is a top gem. Tone should be between 65-85. Average brilliancy should be 50% or greater. Proportions and finish should be good (6) or better. You do not want 5.5 colors or 90 tone gems.

Over the past 25 years, Campbell and Judith Bridges have been promoting and marketing Tsavorite worldwide. Mr. Bridges has written many articles for trade and commercial magazines, such as JQ, JCK, Colored Stone Magazine, Msafiri Magazine, & Vogue. He was a speaker at the GIA International Symposiums in 1981 and 1991, lectured at the Tucson Gem and Mineral Show in 1981, The Precious Stones Congress in Tel Aviv in 1983, chaired a panel and gave a presentation speech at the International Colored Gemstone Association Congress in Bangkok in 1987 and was the Kenyan guide and advisor to National Geographic's correspondent in 1991 for a gem article.

References

The Gem Forecaster” webpage:  www.preciousgemstones.com/gffall96one.html

International Colored Gemstone Association web site: www.gemstone.org/gem-by-gem/english/tsavorite.html

Africa's Secret Treasures, Tsavorite From Kenya: http://www.preciousgemstones.com/gfspr02.html#port

 

Members' Gallery

     Here is where DMS Members can add their Tsavorite photos to share with us.

 

Until Next Time

     We hope you have enjoyed our visit with Tsavorite.  Please join us next month,
when we expect to see another favored Mineral-of-the-Month!
     Until then, stay safe, and happy collecting. hardhat2a.gif (5709 bytes)

 

 

Article Contributors

Photo & Graphics Credits

I would like to gratefully acknowledge the generous contributions of our fellow tsavorite
enthusiasts, collectors, authors, curators, professionals, and club members who made this
work possible. 
Thanks.

Wikipedia.org

ICA Gem Bureau Idar-Oberstein

Campbell and Judith Bridges, Tsavorite USA, Inc.

Isaias Casanova, IC Minerals


2006  All contributions to this article are covered under the copyright protection of this article
and by separate and several copyright protection(s), and are to be used for the sole purposes of
enjoying this scholarly article.  They are used gratefully with express written permission of the
authors, save for generally-accepted scholarly quotes, short in nature, deemed legal to reference
with the appropriate citation and credit.
  Reproduction of this article must be obtained by express
written permission of the author, Kenneth B. Casey, for his contributions, authoring, photos, and
graphics.  Use of all other credited materials requires permission of each contributor separately
.

Links and general contact information are included in the credits above, and throughout this article.
The advice offered herein are only suggestions; it is the reader's charge to use the information
contained herein responsibly.  DMS is not responsible for misuse or accidents caused from this
article. Guest authors bear full responsibility for the permissions to reproduce any and all work
contained herein.  All opinions, theories, proofs, and views expressed within this article, and in
others on this website, do not necessarily reflect the views of the Delaware Mineralogical Society.
 

karissa.jpg (2366 bytes)   
About the Author:  Karissa is the current President of the Delaware Mineralogical Society.  She is also a member of the Tuscarora Lapidary Society (TLS), and is an accomplished lapidarist and collector.

She also has affiliations with other mineral and fossil clubs in the eastern United States, and encourages folks of all ages on the enjoyment of our hobby.

E-mail: kdhendershot@delminsociety.net


Invitation to Members

Members,

Want to see your name in print?  Want to co-author, contribute, or author a whole Mineral of the Month article?  Well, this the forum for you!

And Members, if you have pictures, or a story you would like to share, please feel free to offer.  We'd like to post them for our mutual enjoyment.   Of course, you get full photo and author credit, and a chance to reach other collectors, hobbyists, and scientists.  We only ask that you check your facts, give credit where it is due, keep it wholesome for our Junior Members watching, and keep on topic regarding rockhounding.

You don't even have to be experienced in making a webpage.  We can work together to publish your story.  A handwritten short story with a Polaroid will do.  If you do fancier, a text document with a digital photo will suit, as well.   Sharing is the groundwork from which we can get your story out there.

Our club's webpages can reach any person surfing the net in the world, and even on the International Space Station, if they have a mind to view our website!

We are hoping for a possible tie-in to other informative programs upon which our fellow members might want to collaborate.  Contact me with your suggestions.

Our next MOTM will be a surprise.  For 2005-6, we are waiting for your suggestions.  What mineral do you want to know more about?

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____________________________________

Most of the Mineral of the Month selections have come from most recent club fieldtrips and March Show Themes, and from inspriring world locales. thus far.  If you have a suggestion for a future Mineral of the Month, please e-mail me at: kencasey98@yahoo.com, or tell me at our next meeting.

 

 

Past Minerals of the Month
April 2006 Mineral of the Month: Variscite
March 2006 Mineral of the Month: Petrified Wood, Part II
February 2006 Mineral of the Month: Petrified Wood, Part I
January 2006 Mineral of the Month: Strontianite by Karissa Hendershot
December Mineral of the Month: Clinozoisite
November Mineral of the Month: Bismuth
October Mineral of the Month: Wulfenite by Karissa Hendershot
September Mineral of the Month: Turquoise
August Mineral of the Month: Peridot
July Mineral of the Month: Ruby
June Mineral of the Month: Antarctic Fluorite
May Mineral of the Month: Dolomite, Part 2
April Mineral of the Month: Dolomite, Part 1
March Mineral of the Month: Calcite
February Mineral of the Month: Agate
January Mineral of the Month: Fluorite
December Mineral of the Month: Pyrite
November Mineral of the Month: Stilbite  
October Mineral of the Month: Celestite   
 

This page last updated:  February 19, 2011 10:14:48 AM

 

       

  


Next Meeting
 

April Program, Monday, April 8, 2013:

"Destruction of the Fossil Exposures in the Chesapeake Bay Area" presented by Dr. Lauck Ward

General Club Meeting:
April 8, 2013
(Monday)

We are meeting at
Greenbank Mill


Special Meetings:
 

*Show Committee Meeting, April or May, 2013

*New Home/Lapidary Committee, 2013

*Board Meeting,  April, 2013

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Next Show
DMS March Show
March 1-2, 2014 at DelTech Stanton

 


Our 2013 Show Theme was:
"All That Glitters is as Good as Gold!"

March Show 2013 Report

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Fossil Forum


"Dinny, the Dino"

"Belemnites are coming"

 

MOTM June also commemorates our 50th Show!

It's shiny, yellow, and is a symbol of 50 Years!Can you guess?

Past MOTM

Collecting Adventure Stories:

"Sunny Brook Crick Goethite" by Joe Dunleavy