HomeMajor Colored StonesRubies and SapphiresInclusions and identification characteristics of winza rubies

Introduction

A completely new type of ruby material has been discovered in Tanzania in the area of “Winza“-Dodoma province. Map of new ruby mine locations in Tanzania are given below:-

 

These rubies are of exceptional beauty and first appeared in the Thai market. Hundreds of dealers and miners are heading to this new mining site at this moment.

Dealers of Winza Ruby in Tanzania

The rubies are of exceptional colors and excellent clarity. 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.

Magnificent Rubies from Tanzania

Materials

GRS (Thailand) made a tour 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.

Dr. A. Peretti sorts the rough Winza-Tanzanian rubies of the GRS collection (approx. 5000ct) for research.

3 Rough ruby crystals from Winza-Dodoma with typical shape and color zoning.

 A set of gem quality rubies from Tanzania are available 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 that includes rich red, slightly bluish red, purplish red and orangey-red colors. The colors differ from those of Burmese rubies which are more shining 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.

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“. 

 

Weight of the famous vibrant red spinels from Tanzania is 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.

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

  1. 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.
  2. Raman Spectroscopy
  3. ED-XRF Analyses for separating the new rubies from Tanzania from synthetic and natural counterparts.
  4. Infrared FTIR spectroscopy for separating heat-treated from unheated Tanzania rubies and identifying the nature of particle inclusions.
  5. UV-VIS-NIR infrared spectroscopy for distinguishing the “Winza“-(Dodoma province) rubies from other origins and synthetic counterparts.
  6. LIBS testing

Results

Inclusion Features

 

Curved long needle inclusions in unheated rubies from Tanzania.

Fluid inclusion feathers composed of pinpoints or irregular fluid inclusion tubes

Large negative crystal with adjacent secondary finger print fluid feather 

Blue to black color zoning was observed in some of the rubies

 

Whitish particles concentrated on growth zones in an unheated Tanzanian ruby from “Winza“-(Dodoma province)

Concentrations of pinpoints and whitish particles in unheated rubies from “Winza“-(Dodoma province) (Tanzania)

 

Flat needles that appear to be hollow tubes and corroded

Opaque and bluish-green crystal inclusions identified as blue amphiboles.

Whitish streamers and beams were present in this unheated ruby from Tanzania originating from “Winza“-(Dodoma province).

Two systems of crossing twinning lamella were present in an unheated "Winza"-Tanzanian ruby.

Isolated patchy blue zones were found in this rough unheated "Winza"-Tanzanian ruby.

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.

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.

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. 

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