FEATURE ARTICLE

GEMGUIDE - 1 - NOVEMBER / DECEMBER 2017

In 1968, Henry Platt of Tiffany & Co. christened the newand remarkably beautiful zoisite gem, tanzanite, tohonor its single-source discovery in Tanzania. The year

2017 marks the 50th anniversary of its discovery and is themost notable and exciting event of the gemstone industryof the 20th Century.

What makes this gemstone even more interesting andunique and sets this beautiful stone apart from all others isits remarkable rarity. Crucial in understanding its rarity, is thatthis stone is the only (or, one of the few) that evolved frombeing a collector’s stone and only available to a few, to be-coming a commercially available stone. But this is only for alimited time, namely our generation. Tanzanite is found andmined in only one place on earth, a 7 km2 area that outcropsnear the town of Merelani in northeast Tanzania.

It is found in only one place on earth because of a verycomplex and unique set of geological conditions that cametogether during the breakup of the supercontinent, Gond-wana, between 1.5 and 2.5 billion years ago. My intentionis not to get too technical, but the geological origins are sointeresting, and for me, the start of the story that I want toshare, creating excitement for current and future ownersand to highlight the fact that this gemstone may only beavailable for a single generation.

COLOR AND CAUSESThe most striking feature of tanzanite is its color—or colors.It is a pleochroic gemstone. More specifically, a trichroic gem-stone meaning that it naturally displays a different color ineach direction, or on each axis. The fine crystals display in-tense, well-saturated and deep colors. The color-causing ele-ment (or chromophore) of tanzanite is vanadium. It isresponsible for the blue-violet color in tanzanite. If any geo-logical history needs to be mentioned, it is this, because therare availability of the vanadium during tanzanite’s formationis what ultimately is responsible for what makes this gem-stone so beautiful, desirable and popular.

The vanadium is a trace element that came from the organic(tree and plant) material that was deposited with eroded sil-ica-rich sands and calcium-rich (shell and ocean-life) material

in a deltaic/shallow sea environment that was deposited overmillions of years during the gradual break up of Gondwana.This accumulation of layers was subsequently buried andmetamorphosed at high temperatures and pressures. The or-ganic material became graphite, the silica-rich sands becamethe schists and gneisses, and the calcium-rich material be-came dolomite (an impure marble). All these rocks are seenin the deposit. At 500 million years, a geological event re-sulted in the crystallization of tanzanite. Erosion on the sur-

face on the earth and the natural upliftment of continentalcrust (in respect to the denser and heavier oceanic crust)brought this deposit to the earth’s surface where tanzanitewas found for the first time in 1967.

Tanzanite is part of the orthorhombic crystal system. As tan-zanite extracted from the earth is often in its perfect rectan-gular crystal shape, it is easy to see its trichroism. Thesenatural rough crystals can show either a 3-colour trichoismcombination of blue, violet and brown (combination ofred/yellow/green) or a 3-colour trichroism combination ofblue, violet and violet (so two violet axes, or sides), respec-tively. The reason for the two combinations of trichroism isdue to natural (in the ground) heating that a percentage of

THE RARITY OF TANZANITE

Robert Gessner, BSc (Geology), GG (GIA)

In 1967, blue-violet crystals of the mineral species, zoisite, were discovered south of Mount Kilimanjaro innortheast Tanzania. The host rocks of the discovery, which are orders of magnitude older than Africa’s highestmountain, form part of the Lelatema Mountains and are located very near to the town of Merelani.

FIGURE 1.Tanzanite crystal with calcite, quartz and graphite (associatedminerals) in a pocket with geological hammer for scale. Photo by RobertGessner.

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the natural crystals were locally subjected to. The naturalheating has removed the original red/yellow/green to becomecolorless, and so the (second) violet color is seen.

Technically, this has been achieved by an inter-valance chargetransfer during heating, so Ti3+ (red/yellow/green) changes toTi4+, which is colorless. As all chemical equations require tobe balanced, V4+ changes to V3+, and results in a strongerblue-violet hue. The color change due to heating is a stablechange. As this heating does take place naturally, it is impos-sible to distinguish between post-extraction (or by man). Theresult of this means that there are only two realities to labela tanzanite gemstone as no heat or no heat treatment byman. The first is that the gemstone in question displays itsblue, violet and brown trichroism. The second condition is thata strict and traceable provenance of no heating by man hastaken place of a blue, violet and violet trichroism gemstonedirectly from the earth, through the trade to thewholesaler/retailer. This second condition may be a potentialoption but is strictly tied to a person’s honesty, because it isscientifically impossible to prove.

MINING AND AVAILABILITYThe transition from a collector’s stone to being commer-cially available started in earnest in the late 1990s whenthe Tanzanian government started adequately regulatingthe deposit by sub-dividing the 7-kilometer section intoBlocks A, B, C, D and D-Extension, respectively, and thegranting of mining licenses to companies and individualsat different levels of investment ability. Block C, thelargest of 2 km2 of the 7 km2, was awarded to AfricanGem Resources Limited (Afgem), a private South Africancompany, after winning the tender in 1998. Only in theearly 2000s, did the company start investing heavily in thegeology and mining, as production was decreasing and

becoming more haphazard after an initial and significantbulk sample that raised millions of dollars for Afgem.

The investment in the geology and mining resulted in a betterunderstanding of the deposit’s geology and the tanzanite-bearing structures, and in turn increased the company’s pro-duction. The increased production resulted in increasedrevenues that were put back into the mining. More shaftswere sunk, more mining faces were created and from a ge-ological point of view, more geology was exposed on thesidewalls. With all this work, a geological model was created,as well as an understanding that was never in place before.Another result was that production areas could now be proac-tively planned as opposed to a history of reactive mining. Es-sentially, we were able to get the mining into the right places.As a result, from 2005 to 2006, production from the companyimproved to more consistent commercial volumes. It mustbe noted that at no point can a geologist be predicting thegemstone; we are always predicting the geology in which thegems are formed.

From mid-2000, the consistent production from the minewas as a result of having the mining faces in the right areas.If one face was not producing, another one was. In late-2004,Afgem become a publicly traded company, TanzaniteOneMining Limited (TanzaniteOne), and listed on the London Al-ternative Market (AIM).

Large-scale mining operations generate not only more vol-ume of production, but also more volumes of all grades,more consistently. As a result, a master grading set wascreated. For the first time, rough tanzanite could beparceled for size, color and quality to its sightholders. Bydefinition, this system of product presentation for roughsales could only work with regular and good volumes of

FIGURE 2. Folded layers of metamorphic rock within the tanzanite deposit.High temperatures and pressures created the conditions for this folding.Younger oxidizing conditions have resulted in the iron oxide staining withinall the fractures. Photo by Robert Gessner.

FIGURE 3. Rough orthorhombic tanzanite crystals showing the trichroicpleochroism in transmitted incandescent cap lamp light. Photo by RobertGessner.

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production from the mine. This was as a direct result dueto the size of the deposit being professionally mined, withregular production and future exploration.

Prior to the 2000s, tanzanite did experience a robust trade,chiefly in North America and the Caribbean but extendinginto Europe and Asia. (The GemGuide priced tanzanitesince its inception in 1982.) More formal marketing and dis-tribution started first with Afgem, but then TanzaniteOne,increasing its commercial availability around the world. Butthe story does not end there. Just because it is commer-cially available does not mean that tanzanite is any less rarethan it originally was. The most common understanding of

this single generation concept is that the deposit gets phys-ically exhausted (mined out). However, the actual conceptis that the costs to mine become too high versus the in-come from sales, i.e., the gemstones are still in the groundbut are physically too deep to mine and therefore, too ex-pensive. This factor highlights its generational rarity, whichthe current market and value of tanzanite does not indicate.The market and consumers think that because there arehigh volumes of tanzanite available at the moment that thiswill continue, but this not the case.

RARITY/PRICING/FUTUREThe current prices of tanzanite, particularly at the wholesalelevel, are actually too low for how rare the gemstone is, andtoo low for future mining. The amount of tanzanite on themarket currently should be seen as a bubble and tempo-rary, and will not continue. There has been a lot of recentsupply due to many miners being in the right areas and pro-ducing, with this product subsequently making it to thewholesale market. This is the reason for the low wholesaleprices, but with the mines getting deeper, and the natural

pocket effect of tanzanite, this will not continue and the re-ality is that the deeper the mines get, the more expensiveit will be to mine. For future years of supply, the wholesaleprices do need to increase.

Single generation is a phase coupled to tanzanite since itsmarketing in the 2000s, and this itself, evokes its own ro-mance, beauty and rarity. Trying to tie the availability to anumber of years should not be the discussion point, and inmy opinion, less importance and significance should begiven to it. The history to the talk of only available for an-other 10 years, or 15 years ties in to large scale public min-ing companies attempting to quantify its resource for valuepurposes and investment, which the previous owners inthe 2000s took to the market to create desire and indicateits rarity. There are too many factors that affect the predic-tion of years left to mine, so it should only be seen as aguide and to which less importance should be given. Noone asks how many years left of the Colombian emeralddeposit, or the Burmese ruby deposit? It cannot be defined,so why should the Tanzania Tanzanite deposit be focusedon? The famous Brazilian Paraiba tourmaline and Russiandemantoid garnet deposits are now mined out, and very lit-tle or no material is available anymore; nothing significantin the recent years anyway. Old stock or old mined materialthat does become available command extremely highprices today.

Another wonderful and valuable characteristic of tanzaniteis that there is only natural tanzanite in existence. Man can-not create tanzanite, and this is due to its unique formationin the earth, and its chemistry. Imitations, by definition areany material that looks like a natural gem and is used in itsplace. They do exist but any trained gemologist would beable to confirm whether it is natural or not with a few sim-ple gemological tests.

A rare gemstone with both a remarkably unique geologicalhistory and a success story into the jewelry market andinto our homes. A story of rarity that needs to be shared,a story that is hidden within each piece of tanzanite wornby its owners. u

About the Author: Robert Gessner is a geologist by pro-fession with a BSc Degree in Geology from the Universityof Cape Town (UCT), South Africa (2002), and a post-gradu-ate Honors Degree from the University of Stellenbosch,South Africa, (2004). His first industry opportunity was inTanzania in 2003. He has more than 13 years of coloredgemstone geology and mining experience in East Africaworking specifically with tanzanite, tsavorite, and Zambianemerald. In 2016, he earned his Graduate Gemologist de-gree (GG) from the GIA in Carlsbad, USA. Now based inLos Angeles, his business offers consulting, training andgemstone sourcing. www.gessnergems.com

FIGURE 4. My very first photograph underground in the Block C tanzanitemine. Notice the blue-violet color (without any brown) in the mine afterbeing extracted for the first time after 500 million years in the earth. Photoby Robert Gessner.

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