Home   |  Gemstone Guide   |  Semi-Precious Gem Guide   |  Organic Gem Guide


Gemstones: Paraíba & Cuprian Elbaite



Paraíba & "Paraíba-like" Tourmaline


Rough & Cut Paraíba & Cuprian Elbaite Crystals


Source (Cuprian Elbaite): Brazil (Paraíba, Rio Grande do Norte), Mozambique, Nigeria


Article Copyright © 2008 AllAboutGemstones.com

Paraíba is an extremely rare form of elbaite tourmaline that is "cuprian," or "copper bearing," which can occur in vivid, highly-saturated colors ranging from cyan-blue to emerald-green and violetish-blue to purple. The name "Paraíba" refers to the Brazilian region where cuprian elbaite was first identified. The three principle distinctions of a "Paraíba" tourmaline are: 1) deep color saturation, 2) a unique blue-green hue, 3) lack of 'extinction of light' (absorption of light); all of which contribute to the intense, neon color of the stone.



Within the gem world there is much controversy and debate over the name "Paraíba," and how it should be used to describe copper-bearing elbaite tourmaline that has been discovered in other parts of the world. Hopefully, this page will demystify, and clear up some of the commonly-held misunderstandings that surround this fascinating gem.


The Discovery of Cuprian Elbaite

It appears that the first work on Elbaite that was found to contain copper was done in the 1930s, based on emission spectrography analysis of tourmaline from the island of Elba (see"Spectrographic Analysis of Tourmaline from Elba. It was during this period that copper was first proposed as a chromophore for blue Elbaite. This was provocative, but not definitive work, and the gem trade was not effected by this discovery.

The advent of the ion beam analyzer (IBA) made partial analysis of Elbaite routine. The ion beam analyzer is a non-destructive, and convenient way to get quantitative data for elements that have an atomic number which is higher than carbon. The IBA is limited by the number of preset and programmable channels that can be operated at one time. With the advent of the 'Energy Dispersive X-Ray Fluorescence' (EDXRF) spectrometer, the EDXRF became the preferred method of qualitative chemical analysis of tourmaline since it can sense a wider range of elements at one time.



Paraíba-like Tourmaline

Mounted Paraíba-like Tourmaline

   Purple Cuprian Tourmaline

Purple Cuprian Tourmaline (photo: Jeffrey R. Smith)


These advancements in emission spectrography analysis confirmed the presences of copper in tourmaline, but the significance of copper in Elbaite was not appreciated by the gem trade until the discovery of 'cuprian Elbaite' at Mina da Betalhia in the state of Paraíba, Brazil in the late 1980s. It was quickly determined that copper in the form of Cu2+ was the principle, but not exclusive cause of the unusually saturated shades of green, blue and purple colors.


Paraíba from São José da Batalha

Cuprian Elbaite from Brazil was first identified in the late 1980s by a prospector named Heitor Dimas Barbosa, at the Mina da Bathalha in São José da Batalha, north of the town of Salgadinho, in the state of Paraíba, Brazil. This vivid-blue to greenish-blue variety of Brazilian cuprian Elbaite became generically known as "Paraíba" (also known as "paraibaite," or the less desirable "heitorite" after its discoverer, Heitor Barbosa).



Map of Brazil

   Map of Paraíba Mines


Elbaite

Elbaite is a name for a naturally occurring chemical (mineral) that is grouped with similar chemicals into a category called "tourmaline." It is a complex lithium-bearing sodium aluminum boro silicate, and is the principle member of the "tourmaline group" that is cut into gemstones. Tourmaline comes in all colors of the spectrum, and many combinations of colors (bi-colored, tri-colored) with pink and green being the most common colors used as gemstones.


Cuprian Elbaite Crystal Structure

Most tourmaline specimens have a more saturated color down the c, or "principle axis;" and a different shade of that color, or a completely different color perpendicularly to the c axis (the a/b axises). The color of the a axis and the b axis must be the same because of the geometry of the crystallization of tourmaline.


'Copper-Bearing' Cuprian Elbaite

The term "Cuprian" Elbaite refers to elbaite with copper (copper-bearing) as the principle chromophore. A chromophore is either an element or physical structure in a substance that produces color. To be considered "copper-bearing," or "cuprian" the tourmaline needs to contain at least a trace amount of copper. The list of elements that can be incorporated into tourmaline includes most metals, primarily consisting of copper, manganese, titanium, iron, vanadium and chrome. A notable exception is gold, which has never been found in Elbaite, even in trace amounts.


Cuprian Elbaite Crystallography, Chemistry, Physical Properties

Crystal System trigonal
Crystal Habit parallel elongated, striated - asymmetrically terminated
Specific gravity (SG) 3.03 - 3.25
Mohs Hardness Scale 7.0 to 7.5
Toughness fair to good
Fracture uneven, small conchoidal
Cleavage indistinct
Streak white
Chemical Composition Na(Li1.5Al1.5Cutrace)Al6(BO3)3Si6O18(OH)4

Cuprian Elbaite Optical Properties

Optical Properties double refractive, uniaxial negative
Refractive Index 1.61- 1.65
Birefringence -0.018 to -0.040
Pleochroism moderate to strong
Surface Luster vitreous to resinous
Diaphaneity transparent to translucent
Gem Color blue, green, purple


Color in Cuprian Elbaite

Blue Cuprian Elbaite: The blue hue is caused by copper in the form of Cu2+ residing in the y crystallographic site. This produces two broad bands of absorption centered on wavelengths of approximately 695 nm and 940 nm in the spectrum. Copper's absorption in the red area of the visible spectrum is sufficient to produce the cyan-blue color in tourmaline without any additional chromophores.

Green Cuprian Elbaite: The green hue is caused by manganese in the form of Mn2+ and titanium in the form of Ti4+, when in the presence of a low concentration of iron, and with both elements residing in the y crystallographic site. They combine their electron configurations to produce an IVCT (intervalence charge transfer effect). This effect, which increases the absorption of frequencies of light toward the ultraviolet end of the spectrum, when combined with the copper absorption peak at about 695 nm, has been proposed to produce a greenish coloration. More recently, iron in the form of Fe3+ has been determine to be a chromophore that produces a greenish coloration in cuprian Elbaite.



Purple Cuprian Elbaite: The purple hue is caused by manganese in the form of Mn3+ which produces an absorption peak at about 515nm in the spectrum. This lies within the green range of the visible light spectrum and when combined with the copper absorption peak at about 695 nm produces a range of purplish colors including violet, purple blue and purple in cuprian Elbaite.

The gem industry has historically placed less value on purple specimens which have been heated to change the color to a traditionally accepted "paraiba-like" color of cyan or greenish-blue. This trend may be changing as the allure of "natural" untreated stones gain popularity.


Other Colors of Elbaite that can be Cuprian

All colors of tourmaline can in practice have trace amounts of copper. In colors other than "paraiba-like" colored tourmaline, copper can sometimes produce a different overtone, or an unusual color shift when viewed under different light sources.






The controversy over Paraíba, cuprian Elbaite & "Paraíba-like" tourmaline

by Bruce A. Fry


Cuprian Elbaite from Mozambique

The first laboratory report of copper in tourmaline from Mozambique was made by the GIA in the Lab Notes section of the fall 2004 edition of their magazine Gems and Gemology. The discovery of this specimen was made at the Mavuco mines in the Alto Ligonha pegmatite district, in the Nampula Province of north-eastern Mozambique. Mavuco's cuprian Elbaite is found in the form of alluvial pebbles that are hand-excavated from ancient riverbeds, as opposed to cuprian Elbaite form Paraíba which is primarily found in situ.



Mozambique Map

   Cuprian Elbaite

Tourmaline Mine in Mozambique - © BrianNorton.com


The 2004 GIA determination was made on material provided by me, in the hope of discovering why some of my gem specimens demonstrated a reverse Alexandrite color change. This discovery was both the result of my years of searching for unusual tourmaline colors, and one of the harbingers of a significant gemological event - the revelation that some material produced at Mavuco may be cuprian. This was a revelation because Mavuco had been producing mostly included, unusually colored tourmaline for sometime.

Some of the gem colors produced at Mavuco, and perhaps other locations in Mozambique, were similar to Paraíba, but went untested do to the lack of success in past efforts, the lack of inexpensive laboratory analysis, and the belief that cuprian Elbaite was unique to Paraíba, Brazil. I was finally driven to submit my best example of the reverse Alexandrite color-change tourmaline through Noel Rowe because of the unique properties of the gem, rather than determining its copper content.



Mavuco Mines in Mozambique

Mavuco Mine in Mozambique - © BrianNorton.com

   Mavuco Mines in Mozambique

Mavuco Mine in Mozambique - © BrianNorton.com


Other examples of tourmaline with a more recognizable cuprian Elbaite color remained untested for the previously stated reasons. One of these stones which has since been shown to contain copper, along with the aforementioned color-changing tourmaline which I have come to call Laurelite, were specimens in my collection years before the discovery of cuprian Elbaite in Mozambique.

Another example of the early history of cuprian Elbaite before it was discovered at Mavuco was the purchase of a parcel of two alluvial pebbles from Brian Norton, a long time dealer in facet rough from South Africa. The parcel contained a forty carat pebble of a bright purple color (photo below, left - 16.66 carat faceted) that had never been seen be either one of us before, and a fifteen carat pebble of a strongly dichroic gem with a saturated green c axis, and a completely sky blue a/b axis. All of this occurred before copper was identified in Elbaite from Mozambique.



Purple Cuprian Elbaite from Mozambique

Mozambique cuprian elbaite (photo: Jeffrey R. Smith)

   Blue Green Cuprian Elbaite from Mozambique

Blue & Green Cuprian Elbaite from Mozambique


In a 2004 GIA Gems & Gemology article entitled "Field Study of Paraíba-type Tourmaline Mines in Mozambique," authors Brendan Laurs and Hanco Zwaan detail the discovery of a Paraíba-type tourmaline deposit located near the eastern border of the Alto Ligonha pegmatite district, near the village of Mavuco in northeastern Mozambique. According to this 2004 article, and a subsequent 2008 article in Loupe Online, cuprian Elbaite from the Mavuco deposit was first identified by Moses Konate of Mozambique Gems.


Cuprian Elbaite from Nigeria

A new deposit of cuprian elbaite has been identified in Nigeria, consisting of small, broken crystals. The GIA made the announcement based on 12 cut stones that were supplied to them, the largest being 4 carats. So far, it is impossible to determine whether this material is alluvial, or in situ material.

This is the first time that Nigeria has produced purples, blue-greens, etc. that are similar to the original, highly saturated Paraíba specimens. These new Paraíba-like cuprian elbaite gems have low lead which is closer to the original Paraíba's chemistry.


Cuprian Elbaite from Afghanistan, Madagascar & Namibia

Since the discovery of Paraíba tourmaline at the mina da Batalha in the state of Paraíba, Brazil, the search for more cuprian Elbaite has been intense. With the original deposit mined out and the two deposits discovered in the adjourning state of Rio Grande do Norte producing only limited amounts of material, the best Paraíba tourmaline has reach very high prices and continues to be in demand. Blue-green Elbaite that displays paraiba-like colors which are not the result of copper has been found in such diverse locations as Afghanistan, Namibia and Madagascar, but failed to have copper when tested.



Tourmaline Mines in Namibia

Tourmaline Mine in Usakos, Namibia - © BrianNorton.com

   Tourmaline Mines in Namibia


The most notable of these failed searches for copper-bearing Elbaite was the highly publicized discovery of saturated bright blue-green Elbaite from Afghanistan and Pakistan which was declared to be Paraíba-like until testing showed it did not contain copper.


Reverse Alexandrite Color-Change in Cuprian Elbaite

An unknown, and probably small percentage of cuprian Elbaite appears violet in daylight (cool light), and blue-green in incandescent light (warm light). This is the only known substance to demonstrate this direction of color change, which is the reverse of Alexandrite, the standard for color-change gemstones. According to GIA, the only chromophores present in the gems are copper and manganese. As yet, science does not have an explanation for this color change.


Paraíba, 'Paraíba-like' and Legal Disputes

Much of the controversy and confusion surrounding "Paraíba" results from the correct, or incorrect use of the word "Paraíba" to identify cuprian Elbaite. The Paraíba controversy may have some similarities to past legal disputes over the use of the name "Champagne" in describing a particular variety of California sparkling wine. The essence of the Paraíba dispute lies in the use of the name to describe a mineral, or a region.

A lawsuit was filed by the present owner of Mina da Batlha against a group of world class gemological laboratories over the definition of "Paraiba" tourmaline. It is my understanding that the mine's owner feels he has suffered an economic lose because these laboratories have proposed to put on their certifications that a tourmaline with a similar chemistry and appearance to Brazilian Paraíba tourmaline be identified as "Paraiba" tourmaline, despite its location of origin. The laboratories contend that the definition is necessary because of the difficulty in determining the location of origin for the tourmaline in question. Some gem labs have resorted to the use of the terms "Paraiba-like" or "Paraiba-type" to describe cuprian elbaite originating from outside of Paraíba, Brazil.



Mozambique Windex Blue Cuprian Elbaite

Windex blue cuprian elbaite (photo: © AfricaGems.com)

   Mozambique Purple Cuprian Elbaite

Mozambique cuprian elbaite (photo: © AfricaGems.com)


The $120 million lawsuit was filed on April 7, 2008 in the Superior Court of the State of California, Santa Cruz. In the suit David Sherman, chief executive officer of Paraiba.com, is claiming that "the good name of Paraíba itself has been hijacked," and is seeking both monetary and punitive damages against the American Gem Trade Association, Gemological Institute of America, Brazil Imports Inc., and several individuals [16, 17].

No matter which side of the dispute your interests lie, the gem trade's inadvertent choice of the name "Paraíba" as a description for a particular type of tourmaline has certainly turned out to be a poor choice. This is because very similar, if not identical material has been found in several other locations, and it has proven scientifically difficult to separate similar gems coming from different geographic locations. Additionally, not all tourmaline from Mina da Batalha are cuprian, and therefor can not be called Paraíba.

Certainly, the story of the Mina da Batalha has some value romantically, but letting the quality of each individual gem make the price for those lucky enough to own one seems the only reasonable, and viable option. I hope that all grades of tourmaline are compared from all sources of tourmaline and that each gemstone be valued by its qualities and demand, rather than visually, or chemically identical stones receiving different pricing treatment.


Heat Treatment of Cuprian Elbaite

All deposits of cuprian Elbaite produce a suite of colors that are unusual for tourmaline with the purple-blue to purple shades being the rarest color in the complete spectrum of colors displayed by tourmaline. Their rarity and beauty did not prove to be enough to compete with the popularity of cyan-blue Elbaite and they have been traditionally heated to reduce Mn3+ to Mn2+ to eliminate the purple shade and produce cyan-blue Elbaite. Even rich purples similar to Siberian Amethyst were heated and this proved to produce some of the best cyan-blue Elbaite gems. Other colors such as grayish-blue-greens were also heated to enhance their color, but this was not always successful.

The normal temperatures used in the heating of cuprian Elbaite does not effect copper's oxidation state and contribution to the gems color. The majority of emerald-greens found in cuprian Elbaite are produced by heating, but they can also occur naturally. Colors achieved by heating cuprian elbaite are permanent. Some tourmaline is not capable of being heated due to the presence of internal flaws such as growth tubes, feathers, and other internal imperfections.


Are Colors Produced by Copper in Tourmaline Unique in the Gem World?

No, copper does produce unusual shades of color in tourmaline, but other gemstones can closely approximate cuprian Elbaite colors. This includes emerald for bluish-green, sapphire and tanzanite for bluish-purples, and apatite and flourite for cyan-blue. You may note that both apatite and flourite, while faceted into gems, are too soft and fragile to be durable gemstones and are really only suitable for collectors. Tourmaline is a durable gemstone in all its colors.


Testing and the Future of Paraíba & Cuprian Elbaite

Traditional 'wet chemistry' testing of tourmaline is difficult and expensive because tourmaline is completely insoluble in common acids under normal conditions. The advent of EDXRF has made partial analysis of tourmaline routine, but has proven inadequate in classifying cuprian tourmaline by its geographic origin. Recent announcements that some testing laboratories can determine, in many cases, whether a specimen of cuprian tourmaline is from Brazil or Nigeria or Mozambique is based on the use of a LA-ICP-MS (Laser Ablation, Inductively Coupled Plasma, Mass Spectrometer) which is relatively new to gemological testing.

Another new development in the testing of cuprian tourmaline is the use of inexpensive yet sophisticated spectrometers to determine if the level of copper found in the tourmaline is actually influencing the color of the gemstone. The monetary implications of correctly identifying and/or naming a specimen as either copper-bearing tourmaline, cuprian elbaite, or Paraíba could force the jewelry trade to become increasingly dependent on the use of analytical tools like EDXRF and LA-ICP-MS, and this additional cost will most likely be passed on to the consumer.






Bibliography on Paraíba & Cuprian Elbaite


1. MSA, Color in Cuprian Elbaite . www.minsocam.org

2. Wendell E. Wilson, Cuprian Elbaite from the Batalha Mine, Paraíba, Brazil . www.minrec.org

3. GRS, 'Paraíba' Tourmaline Research Completed . www.gemresearch.ch

4. Brian Norton, Toumaline Gemstones from African . www.briannorton.com

5. Brendan M. Laurs, Exotic Beauties of Mozambique GIA

6. Brendan Laurs, Hanco Zwaan, Paraíba-type Tourmaline Mines in Mozambique GIA

7. Jason Stephenson, The Path to Paraiba Winds Through Mozambique Palagems

8. Richard W. Wise, Mozambique Cuprian Tourmaline . gemwiseblogspotcom.blogspot.com

9. Robert Genis, Mozambique Tourmaline Hits the Market . www.preciousgemstones.com

10. Richard W. Wise, Cuprite Tourmaline from Mozambique . www.diamondchitchat.com

11. American Mineralogist, The Origins of Color in Minerals . www.minsocam.org

12. Mineralienatlas, Das Gebiet Minas Gerais . www.mineralienatlas.de

13. GIA, Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) . www.gia.edu

14. Brendan M. Laurs, Exotic Beauties of Mozambique GIA

15. TOE Ltd., Brazilian Paraiba Tourmaline . www.paraiba.com

16. A. DeMarco, G. Roskin, Name Blame: Lawsuit over naming of Paraiba . www.allbusiness.com

17. JCK, AGTA Demands Dismissal of $120M Paraiba Suit . www.jckonline.com

18. Africa Gems, Cuprian Elbaite from Mozambique . www.africagems.com





Gemology Books
Gemstone Books


Gem Home   |  Gemstone Guide

  

Copyright © 2012 AllAboutGemstones.com. All rights reserved.

  
  
Gemstone Books
Gemmology and Synthetic Gems