New Important Gem Discovery in Tanzania:
The Tanzanian “Winza“-(Dodoma) Rubies
Contributions to Gemmology No. 7, April 2008
Important editorial comment: GRS announces that the result of this report (see also our discovery of the FTIR characteristics and distinction of heat-treated and unheated rubies using FTIR) as copyright registered by us with the Library of Congress in April 2008 (Case #: 1-66023941) has been confirmed by a recent study published in Gems and Gemology by competing laboratories and a number of associated scientists from France and Germany (Schwarz et al, 2009: Rubies and Sapphires form Winza, Central Tanzania,p.322-340, Gems and Gemology, Winter Issue,2008). As they overlooked to give us credit for our research discovery in their report, we claim herewith at this place ourself ownership of being the first laboratory having reported these important properties. See also Palagems.com, scroll down to article titled "Winza Ruby from Tanzania".
A Special GRS Alert On-line Report* by
Dr. Adolf Peretti
Director of GRS laboratories
* This report is available as a VCD including a movie clip and a PDF file and is copyrighted and registered. ISBN 978-3-9523359-6-3.
Introduction
A completely new type of ruby material has been discovered in Tanzania in the area of “Winza“-(Dodoma province) (see Map).
These rubies are of exceptional beauty and first appeared in the Thai market approx. 2 months ago. Faceted Tanzanian rubies of over 10ct are fetching extremely high market prices.
Hundreds of dealers and miners are heading to this new mining site at this moment.
The rubies are of excellent colors and exceptional clarity. Significant numbers of unheated rubies appeared on the market. Parcels that have been acquired from these new occurrence contained synthetic rubies and first samples of heat-treated rubies appeared in the market as well. Beside rubies, blue sapphires, orangy-pink sapphires (padparadscha) and color-changing sapphires were found (see movie 1).
This is the first report in the literature on the properties and identification of the new ruby material from this mine in Tanzania. It is aimed to help identify these rubies at a critical moment when synthetic or heated materials are potentially mixed in the parcels without disclosure.
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Fig. 1 New ruby mine locations in Tanzania are found in the vicinity of “Winza“-(Dodoma province). |
Expedition Videos
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Video 1 Origin of Magnificent Rubies from Tanzania (5:13 min.)
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Video 2 Magnificent Tanzanian rubies (30 sec.)
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Video 3 New Winza Tanzanian ruby mines visit (1:26 min.)
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Materials
GRS (Thailand) made an expedition to the ruby mine in April 2008 and acquired a large series of rough materials for this report directly from the mine. The rough materials were polished at GRS and form a part of GRS’ reference collection. A series of gem quality rubies which appeared in the market were also included in this study to compare with the collected samples from the mining site. Some of these samples of large faceted rubies of over 10cts were tested before cutting. First samples of heat-treated rubies appeared as well in the market. First checks on the separation of heat-treated and unheated materials by special tests are made but this study will have to be expanded at a later date. The total number of samples analyzed exceeds 200 samples.
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Fig. 2 Dr. A. Peretti sorts the rough Winza-Tanzanian rubies of the GRS collection (approx. 5000ct) for research.
Fig. 3 Rough ruby crystals from Winza-Dodoma with typical shape and color zoning.
Fig. 4 A set of Winza rubies with typical shape and color-zoning selected for research.
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Fig. 5 A set of gem quality rubies from Tanzania with “vibrant red” colors. Note different cutting styles used for unheated Tanzanian rubies from “Winza“-(Dodoma province) (weight range between 3 to 8 ct). |
Color Varieties
The rubies appear in very vibrant colors of pure red, slightly orangy-red or orange-red colors. The colors differ from those of Burmese rubies which are more fluorescent and may have slightly more purplish secondary colors. In GRS’ Reports these rubies are described as “vibrant red” (maximum intensity and excellent brilliancy). If the secondary orange color is above a certain limit, these gemstones are not described as rubies but as orange-red sapphires or fancy sapphires. The GRS-type “pigeon’s blood” color is not applied for the description of these new Tanzania rubies, because of high Fe-concentrations and lower fluorescence as well as the presence of orange component in the red colors.
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Fig. 6a Weights of gem quality faceted rubies tested at GRS. Rubies of over 10ct do occur. Some of the rubies over 5 ct have excellent “vibrant red” color and has been classified as either important or magnificent and 3 rubies over 10 ct were awarded with the “Magnificent Platinum Award of GRS“. |
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Fig. 6b Weights of the famous vibrant red spinels from Tanzania. The spinels are of extremely beautiful vibrant pinkish-red to pure red colors. Faceted Spinels of over 30ct have been tested and have been awarded with the “Magnificent Platinum award” of GRS. A comparison with the rubies shows that these spinels do occur in about 3x larger sizes than rubies which just emerged recently. |
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Fig. 6c Fluorescence of Tanzania ruby (left) and Burmese ruby (right) if exposed to 365nm UV light lamp. The fluorescence of Tanzania ruby is classified as medium to strong and for the Burmese ruby as very strong.
The extent of fluorescence appears weaker in comparison to marble type rubies (Burmese, Afghanistan, Vietnam and Tajikistan) but similar to Thai rubies. Flame fusion rubies in comparison, appear with a stronger fluorescence. |
Methods of Analyses
- Inclusion analysis was carried out for the purpose of providing clues for origin determination as well as providing the details for determining the authenticity of the material and indications for any application of heat-treatment. A detailed Raman and SEM study is currently being undertaken.
- Raman Spectroscopy
- ED-XRF Analyses for separating the new rubies from Tanzania from synthetic and natural counterparts.
- Infrared FTIR spectroscopy for separating heat-treated from unheated Tanzania rubies and identifying the nature of particle inclusions.
- UV-VIS-NIR infrared spectroscopy for distinguishing the “Winza“-(Dodoma province) rubies from other origins and synthetic counterparts.
- LIBS testing
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Results
1. Inclusion features
Fig. 7 Curved long needle inclusions in unheated rubies from Tanzania.
Fig. 8 Fluid inclusion feathers composed of pinpoints or irregular fluid inclusion tubes.
Fig. 9 Large negative crystal with adjacent secondary finger print fluid feather .
Fig. 10 Blue to black color zoning was observed in some of the rubies.
Fig. 11 Whitish particles concentrated on growth zones in an unheated Tanzanian ruby from “Winza“-(Dodoma province).
Fig. 12 Concentrations of pinpoints and whitish particles in unheated rubies from “Winza“-(Dodoma province) (Tanzania).
Fig. 13 Flat needles that appear to be hollow tubes and corroded.
Fig. 14 Opaque and bluish-green crystal inclusions identified as blue amphiboles.
Fig. 15 Whitish streamers and beams were present in this unheated ruby from Tanzania originating from “Winza“-(Dodoma province).
Fig. 16 Two systems of crossing twinning lamella were present in an unheated "Winza"-Tanzanian ruby.
Fig. 17 Isolated patchy blue zones were found in this rough unheated "Winza"-Tanzanian ruby.
2. Raman Spectroscopy
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Fig. 18a First arrival of solid inclusion analyses by Raman spectroscopy: Spectacular orange garnet inclusions are found in the rubies, which are almost never found in gem quality rubies. Left Raman spectrum of garnet inclusion which reaches surface. Analyzed by FTIR-NIR Raman spectroscopy (GRS in-house).
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Fig. 18b Talc (with concentrations of nickel) were found as overgrowth on a ruby from Winza.
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Fig. 18c Hand specimen found in mining site at the exact spot of the ruby occurrences consists of talc (identified by ED-XRF and Raman). ED-XRF analysis revealed concentrations of traces of Nickel in the talc composition.
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Fig. 18d Round colorless inclusion in a ruby from Tanzania (Winza) was identified by ED-XRF and Raman as Flour-Apatite with concentrations of Chlorine (Cl). The contact of the Apatite to the ruby is marked by a thin layer of another mineral phase (reaction rim) which is not yet identified.
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Fig. 18e Blue and green minerals are found as inclusions and on the surface are identified as blue amphibole. The blue amphibole also did have some concentrations of Nickel (Ni). Further analysis of various light green to bluish-green minerals are currently underway. Most of these inclusions were found to be green and blue amphiboles. A detailed analysis will follow later.
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3. Chemical composition: measured by ED-XRF (GRS in-house)
Fig. 19 Chemical composition (Chromium, Iron and Gallium) in comparison to rubies from other origins. The field of Tanzania rubies is highlighted. Note equal iron and chromium concentrations are typical for the new Tanzania rubies. The Chromium to Iron ratio may vary slightly and result in different color varieties (more or less orange component).
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4. FTIR Analysis (GRS in-house)
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Fig. 20a FTIR-Infrared spectra of gem quality Tanzania rubies showed a series of absorption lines related to OH either structural or from mineral inclusions. The strong 3158 wavenumbers line was always present in unheated rubies.
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Fig. 20b A first Tanzania ruby that was heat-treated in a laboratory in Chantaburi did not show theses lines. Heat-treatment may be applied for the purpose of removing blue zones in rubies. A further more detailed report on heat-treatment of the “Winza“-(Dodoma province) rubies will be included at a later stage. It is expected that the FTIR test will be a very important test for separating heated from unheated rubies.
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Fig. 21 Overlapping two FTIR spectra, of a heated Mong Hsu ruby (blue) with an unheated Tanzania ruby (pink). The OH-related absorption lines observed in heated (warmed) Mong Hsu rubies are distinctively different from those of an unheated Tanzania ruby.
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Fig. 22 FTIR spectrum of an unheated Mong Hsu ruby (blue) and an unheated Tanzania ruby (red). They are distinctively different.
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Fig. 23 Infrared spectra of heated Tanzania rubies. Note the difference to the spectra of unheated Tanzania rubies Spectra 20a.
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Rough Tanzania rubies experimentally heat-treated to higher temperatures.
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Fig. 24 FTIR Spectrum of a Ruby from Tanzania, heated at atmospheric conditions at 900°C for 3 hours.
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Fig. 25 Spectra of 2 samples that were experimentally heat treated with the same treatment as the rubies from Mong Hsu (at lower temperatures). Each graph has 2 spectra which are from the same sample before and after heat treatment.
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5. UV-VIS-NIR spectroscopy
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Fig. 26 UV-VIS spectrum of Tanzania rubies is characteristic for a ruby of high iron concentrations. Such spectra are, according to our opinion almost never observed in Burmese rubies but do occur in rubies found in Thailand. Thai rubies and “Winza“-(Dodoma province)-Tanzanian rubies, however, can be easily separated by inclusion analyses and FTIR infrared analyses.
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6. LIBS testing (GRS in-house)
LIBS testing of rubies and blue zones in rubies from Tanzania showed no concentrations of beryllium. Magnesium concentrations are similar those in sapphires from Sri Lanka and Madagascar.
The magnesium concentration in rubies (including blue zones) is generally higher than those of basaltic origin.
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Conclusion
Market importance
The new rubies found in Tanzania from “Winza“-(Dodoma province) deliver a welcomed new addition to the world of unheated rubies of important size and excellent beauty. It is not yet understood how large the occurrence is, but it is clear that magnificent unheated rubies over 10ct in size do occur. Magnificent rubies are spared of thermal enhancement and are of excellent clarity and excellent brilliancy.
Identification
The new ruby material offers a completely new type of inclusions (curved and circled long needles) that have never been found in any other ruby material to our knowledge. These inclusion features can also easily been utilized to differentiate against all types of synthetic rubies known so far. In the absence of long needles microscopic analyses may reveal the presence of fluid inclusion feathers, blue growth zones, and series of green and blue solid crystals, very fine whitish zones of submicroscopic particles or clouds of whitish pin points. Extension cracks emerging from fluid inclusion trails have been detected in heat-treated (“warmed”) rubies. Rutile inclusions (silk) were not present in the “Winza“-(Dodoma province) Tanzanian rubies.
Regarding the identification of the origin of these rubies from Tanzania, the set of inclusion feature in combination with special tests enables a clear separation from rubies from other origins. For example, the inclusion features are completely different to those of Thai rubies which are otherwise chemically more similar to the new Tanzanian rubies.
Unusual large rubies of excellent clarity with the complete absence of any inclusions can be found as well. Their identification needs special analyses, particularly FTIR analyses and ED-XRF chemical analyses.
The chemical compositions of the Tanzanian “Winza“-(Dodoma province) rubies are characterized by equal compositions of chromium and iron. The iron concentrations are slightly lower than those of Thai rubies but much higher than rubies from marble deposits such as Burmese, Vietnamese, Afghanistan and Tajikistan rubies. In terms of chemical compositions, the “Winza“-(Dodoma province) rubies are most similar to those of Thai rubies. Ti concentrations are variable. In general, Ti -concentrations are low. Higher Ti-concentrations are found when blue zones are present in the rubies. Other elements such as Vanadium and Gallium concentrations are very low. In comparison, rubies from marble deposits (such as Burmese rubies) for example, have much higher concentrations in Vanadium and Gallium than the “Winza“-(Dodoma province) rubies.
In conclusion, the chemical analyses can be used to distinguish between most synthetic rubies including flame-fusion synthetic rubies and most of the Flux rubies, with the exception of Ramaura-Thai-type synthetic Flux rubies and some iron-rich synthetic hydrothermal rubies. Additional FTIR spectroscopy may be necessary to separate the “Winza“-(Dodoma province) rubies from synthetic counter parts.
UV-VIS-NIR spectroscopy is characterized by an absorption spectrum with a narrow UV-transmission and the position of absorption edges in the visible region of the spectrum. It mostly resembles those of some Thai rubies but is distinctively different to absorption features found in rubies from other origins, such as Burmese rubies.
FTIR spectrum revealed a series of lines in the region OH-absorption lines around 3158 wave numbers. These Infrared absorptions are in generally not present in other unheated rubies from other origins. The infrared spectrum is closest to those of some unheated Mong Hsu rubies but different from heated Mong Hsu rubies and also different to those of other synthetic counterparts.
In conclusion, “Winza“-(Dodoma province) rubies can be clearly identified and separated from all synthetic and natural counterparts. The identification can be largely based on inclusion analyses. In special cases, a combination of inclusion analyses with special methods (UV-VIS-NIR, ED-XRF and FTIR) is needed. Application of heat-treatment can be investigated by a combination of inclusion analyses and FTIR-analyses.
Formation Conditions
The formation conditions are still under investigation, as the stones were not found in situ.
However, the following important observations were made from the analysis of the inclusions:
- Talc overgrowth was found. The talc contained traces of nickel.
- The most frequent inclusion found so far was a mineral of the amphibole group (blue and green minerals). The mineral contained traces of nickel, as well as Lithium. Amphibole was found as “phantom” precipitations confined to earlier growth phases of ruby. Tourmaline was not confirmed after testing with high tech-instrumentation.
(Most of the inclusions turned out to be blue amphibole after we analyzed them with SEM-EDS analyses).
- Garnet inclusions were found inter-grown with blue and green amphibole. Ruby samples were found that nucleated from a substrate of garnet and amphiboles.
- Extremely rarely, apatite inclusions were found, which contained fluorine and chlorine.
Furthermore, the following observations were made:
- Fluid inclusion trails are very frequently found in the rubies (and sapphires).
- Blue color-zoning (confined to variable Ti-concentrations in the rubies) are found. Extremely fine oscillations of Titanium are present in the rubies.
Based on the analysis of mineral inter-growth of more than 5000 samples and corresponding mineral inclusions, the formation of Winza rubies took place in Garnet-Amphibolites. The rubies were formed from solutions rich in alumina, fluorine, chlorine, sodium, phosphor, calcium, chromium, titanium, iron and nickel solutions. It is evident that dramatic changes in the formation conditions occurred during the formation of the rubies. The composition of the mineral and fluid inclusions will be further investigated to check the pressure, temperature and solution conditions of the Winza rubies.
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