On the field ...

This map shows the places we visited during our missions. Click on the photo to access the corresponding article.

Travelog / MEETING

Australia :
a great gemological heritage

4/4 Australian sapphires, the forgotten

Boris Chauviré; June 2023

Figure 1 : Artisanal mining by hand on the outskirts of Police Knob, an ancient volcanic structure in Rubyvale.

Although Australia is renowned for its opals, and has even made them its national gemstone, sapphire plays an important role in its gemological resources. Sapphire deposits, associated with the basalts found throughout the eastern part of Australia (from north-east Queensland to Tasmania), provided large quantities of so-called volcanic sapphires in the second half of the 20th century. To our knowledge, no Australian corundum has been found in the source rock, but these sapphires have all the characteristics of volcanic origin. Their dominant colour ranges from blue to orange, passing through green and yellow, and they can reach significant sizes (several unheated samples of more than 10 ct have been observed). During the trip, two of the main areas were visited, the first still active (the Anakie region, notably the town of Rubyvale) and the second which was intensively exploited but is inactive today (the New England region, around Inverell).


Rubyvale is a small town ten hours drive west of Brisbane, part of the Anakie gem region. This region was the first to be mined for corundum, at the end of the 19th century (Coldham et al. 1985[1]). Easily accessible, Rubyvale has a population of just over 500[2] and is a well-known tourist destination in Queensland. Although the best known, Rubyvale is not the only one to produce sapphire, as the surrounding towns in the Anakie region (with evocative names like “Sapphire”) also have mines on their soil#. Sapphires are found in eluvial or colluvial deposits (after alteration of the parent rock, but with limited transport). The different types of mining range from small-scale manual mines (Figure 1), where the miner digs a few decimetres below the surface to find the sapphires, to industrial mines such as the Capricorn Mine (located near the Tropic of Capricorn) run by Fura Gems. Although often open-cast, there are a few underground mines, where the sapphires are concentrated in several levels, varying greatly in richness, quality and size. The miners seem to say that the biggest sapphires are found deeper down, close to a pseudo-conglomeratic level at a lithological boundary (unconformity between the granitic bedrock and the sediments?), but the highest quality would be in shallower levels. Although the landscape is intensely eroded, the ancient volcanic edifices that brought the sapphires up are still visible.

Mechanised mines are the most traditional way of mining corundum. The ore is extracted by excavator, then sorted first by size to remove the large blocks of rock, then gravimetrically using water in a jig (a machine that pulses the water from below, bringing up the fine, light particles that are carried away by the water, leaving the denser minerals at the bottom). As water resources are a major issue in this region, the water is recovered and recycled (often after passing through one or more settling basins). The gem-bearing gravel is then sorted, either by machine (magnetic separator) or entirely by hand. Zircons (ranging from colourless to orange-brown) and a few black spinels are also concentrated in this gravel along with the sapphires.

#However, don’t expect to see emeralds in emerald, the county’s largest town, as the name comes from the green of its landscape.


The New England region, in the north of the state of New South Wales, was the first area where sapphire was identified in Australia around 1854 (Coldham et al. 1985[1]). The region enjoyed a boom period in the second half of the 20th century, when Asian traders helped to expand production. It is even said that these traders rented rooms all year round in local motels in order to buy sapphires on a permanent basis and thus supply the market. The great fortunes made from the sapphire trade in Southeast Asia, thought to have originated in Thailand or Cambodia, were partly (mostly?) built on the wealth of Australian deposits. Around the towns of Inverell and Glenn Innes, there were numerous mines, often mechanised and employing dozens of people. Today, however, the only evidence of these mines is the presence of a few shops selling sapphires in the towns in the region. The last mine actually in operation closed a few months before our visit to the region, which can be considered inactive as of 2023. All that remains are a few tourist spots where, for a few dozen dollars, you can look for gems with the help of a former miner.

This region is a good example of the impact of mining on the landscape after several decades of extraction. As a reminder, the mining processes used to extract sapphires in this region involve digging down to depths of dozens of metres and then separating the sapphires from the ore by granulometric and gravimetric sorting.In this process, apart from the products used to maintain the machines or the hydrocarbons for their operation, no other chemical agents are required.This differs greatly from the separation of other ores such as aluminium or copper, which requires products such as soda ash or strong acids.Although pieces of metal can be found in formerly mined areas, the landscape does not seem to have retained much memory of this mining past.The land that has been stripped of its precious gems is now used as fertile soil in this agricultural region, where only a few mounds have been dug up from former excavations.Without knowing the history of New England, it is difficult to see the impact of sapphire mining on this landscape reminiscent of the English counties.

[1]Coldham, T. (1985): Sapphires from Australia. Gems Gemol., 21, 130–146.


Figure 2 : Landscape after the rehabilitation of the sapphire mines in the second half of the 20th century, with no trace of the mines visible.

Travelog / Meeting

Australia :
a great gemological heritage

3/4 Queensland : the opal boulders' state

Boris Chauviré; June 2023

Figure 1 : Top: Opal samples from Yowah, showing an opalised "nut", with concentric layers of opal emphasising the appearance of the concretions. Bottom: an opalised conglomerate (samples from the McGuire collection, exhibited at Yowah).

Head to the north-east of Australia to discover other types of opal: boulder and matrix opals. The majority of opals in South Australia (with the exception of Andamooka) and New South Wales are found in argillite or fine sandstone, where the opal is extracted from the rock and sold without the host rock. In comparison, Queensland opals are found in fissures or veins in ferruginous rocks that are either in the form of concretions, known as “boulders” or “nuts” (a term used in particular for those at Yowah, Figure 1 top), or in the form of conglomerates. In the latter, the opal is both in the small concretions that make up the conglomerate and as the cement that fills the fissures (better known as matrix opal, Figure 1 bottom). These opals are sold as specimens, or cut into cabochons by retaining part of the host rock. During this trip, we were able to visit three areas producing this type of opal: Yowah, a mine around Quilpie and Koroït.


Yowah is a village of around a hundred inhabitants[1] in the middle of the Australian outback, about an 11-hour drive from Brisbane (Queensland’s capital). With a café, mini-market and motel, Yowah has a great reputation for its opals contained in small ferruginous concretions known as Yowah nuts. These nuts are often concentrated in yellow to brown levels of medium to fine sandstone, but they can also be found randomly in the surrounding light sandstone. A first level exists very close to the surface (one or two metres deep) separated by sandstone from a second, deeper level (around ten metres deep) which highlights an interface between the sandstone and a finer layer (argillite) underneath. The levels are not flat, but vary in depth from a few metres to a few metres laterally. The sandstone also has variations in grain size within lenses of a few metres. The colour of the rocks seems to be an indicator of opal richness for the miners.

Miners extract the nuts either using traditional tools (pickaxes, crowbars) or mechanised methods (excavators, hydraulic claws, etc.), both in open-cast and underground mines. Opal can also be found in rock, apart from ferruginous concretions. Separation is often done by hand, and the nuts are broken by hand to reveal the structure, which is sometimes opalised. Miners also harvest the opal-rich sandstone to conglomerate layer (i.e. matrix opals). The opal is found in the fissures of the nuts, and sometimes fills the fissures between the concentric layers of concretions until it completely or partially fills the centre of the nuts. Partial filling shows the orientation of the water level (the horizontal level) in the concretions. To observe the variety of boulder opal from Yowah (and also from Koroït) a collection of samples is on display at Yowah (the Macguire collection).


The Quilpie district, north of Yowah, is a flat area with several dozen mechanised mines. Only a few mesas (small, flat-topped hills) break up the flatness of the landscape. The edges of these mesas are mined for boulders. The mines are sporadic and isolated (at least several kilometres apart), but they are generally well mechanised. The top of the mesas is made up of a very hard, ten-metre-thick siltstone over a medium to fine white to pinkish-red sandstone. The boulders, up to several decimetres thick and several metres long, are randomly distributed over the tens of metres of sandstone (Figure 2). The boulders are concretions, with more or less complex concentric figures, where opal fills the cracks. The sandstone is scraped progressively with an excavator, and the boulders are broken with a sledgehammer to see if they contain opal. Those containing opal are then transported to the camp for sorting. In opalised fissures, the opal may be horizontally stratified.


Figure 2 : Examples of opalised boulders found in a mine near Alaric, in the Quilpie region.

Figure 3 : Major fault observed in a mine at Koroït.


Koroït is a small mining area located to the east between Yowah and Quilpie, close to the town of Humeburn. With a few dozen miners, this extensive area supplies matrix opals renowned for their patterns (often comma-shaped) or small nodules of ferruginous concretions filled with opal forming a conglomerate. However, these patterns are also found in Yowah, and are not indicative of the precise origin, but appear to be specific only to Australian opals from Queensland. Some cavities may be partially filled with opal, and on the same sample we can sometimes observe cavities that are completely or partially filled.

As previously described, these concretions or opalised ferruginous conglomerates are concentrated in one or more ferruginous levels (yellow to brown), separated by fine to medium-light sandstone which may also contain boulders. Miners sometimes observe an inverse granulometry of boulders between the ferruginous levels: the largest boulders are at a shallower depth while the finest are at a greater depth. The last ferruginous opal level is located at the interface between the sandstone and the underlying argillite, at a depth of around fifteen metres.

The mine is mainly open-pit, after prospecting for the depth of the ferruginous levels and the presence of opal by drilling. As at the Quilpie mine, an excavator scrapes the rocks containing the concretions, which are then crushed to assess their opal potential. These large sections also reveal tectonic incidents, such as faults with movements of several metres. Certain ferruginous levels seem to follow these faults, rather than being intersected by them, although miners report finding concretions sometimes opalised in these faults.

With unique patterns emphasised by the contrast between the iron minerals and the play of colour, boulder or matrix opals are attractive specimens. Their use in jewellery today is limited to cabochon-cutting, where the opal veneer is highlighted with the rock behind, often obscuring its geological patterns. For a geologist, it is sometimes a shame not to have these patterns more prominently displayed. Fine examples of these opals can be seen at the Opal Museum in Brisbane, so don’t hesitate to drop in!

Travelog / Meeting

Australia :
a great gemological heritage

2/4 An opal icon: Lightning Ridge

Boris Chauviré; June 2023

Figure 1 : Lightning Ridge, a town dedicated to opal.

After a visit to the opal producing areas of South Australia, it’s time to visit the town with the best international reputation for opals: Lightning Ridge. This town in the state of New South Wales, a 9-hour drive north of Sydney, is the largest opal mining area in Australia, with over 4,000 declared claims and around 850 miners*. With more than 1,300 inhabitants at the last census[1], the town has all the essential amenities for a stay (several motels, restaurants, petrol stations, etc.). Like Coober Pedy, the whole town is dedicated to opal mining and sales, with a dozen or so shops on the main street (Figure 1).

Lightning Ridge owes its reputation in particular to its production of black opals, whose play of colour is enhanced by the dark colour of the opal. The name is so closely associated with this type of opal that black opals from other areas (including Coober Pedy, for example) can be brought to Lightning Ridge to benefit from the aura of the name. The area mined in the district is vast, stretching for dozens of kilometres around the town and including, among others, Garwin, Cocooran and Wyoming. The names can also be evocative, such as Three Miles (located three miles from the town centre) or Sheepyard (referring to an old sheepfold that used to be in the area).

*According to the miners’ association.

As in Coober Pedy, the opals are generally found in horizontal veins in a fine white sandstone with pink, red and even brown levels, which the miners believe are the levels containing the opal (Figure 2). The miners are also looking for evidence of tectonic movements, such as vertical fissures or faults, which would indicate the potential presence of opal. Although most prospecting is done by drilling, some miners use changes or patterns that can be seen in the vegetation. Alignments of trees of particular species are said to be associated with cracks in the rock (which allow vegetation to reach water resources more easily). Opals are also found in the form of ‘nobbies’, flat sandstone pebbles that may contain opal inside.


Figure 2 : Common opal in the rock in an underground mine at Lightning Ridge.

Lightning Ridge is also known for its opalised fossil shells (as can be seen at Coober Pedy), but also for a wide variety of dinosaur fossils (Figure 4). Teeth, jaws and bones forming the ends of pasta have regularly been studied to reconstruct the fauna of the past[2,3].

The richness and renown of this opal-bearing area makes it a prime location for promoting Australian opals. The Australian Opal Centre is a grassroots initiative, funded primarily by opal enthusiasts and/or professionals, and based at Lightning Ridge. The centre is a museum open to the public about opal and the cultural heritage of the Australian outback. Visitors can also take courses or workshops in opal research, fossils and their identification.

The miners’ association enables miners to share the costs of declaring plots of land, as well as the equipment and maintenance of the roads leading to the mines. The association has also set up a committee to evaluate gems and harmonise prices. This committee meets every week and the 5 to 10 members assess the price of a few stones submitted by the miners (each miner is entitled to have up to 5 stones assessed). Each valuation is the average of the value estimated by each appraiser.

Lightning Ridge, although mainly focused on opals, has another special feature. In the middle of the desert, boreholes were drilled to pump water and what are known as artesian wells (named after the town of Lillers-en-Artois in northern France) were discovered. These areas where water naturally gushes out of deep rock are formed thanks to the geometry of the sedimentary basin, with successive layers in the shape of a plate (concave). The aquifers trapped between two impermeable layers of the basin are fed by the infiltration of water in the mountains to the north of Australia. Over a period of two million years, the water will infiltrate the basin, and if a fracture or a borehole is drilled in the middle of the basin (generally at a lower altitude), the water will gush out naturally thanks to the principle of communicating vessels, since the infiltration level is higher than the outflow level. As the water can reach depths of several hundred metres, or even a few kilometres, it will be heated at depth and come back up still hot (around 40°C at Lightning Ridge).

After a day full of dust, rock galleries and opals, a hot bath under the Milky Way is always welcome…

[2]Bell, P.R., Brougham, T., Herne, M.C., Frauenfelder, T., & Smith, E.T. (2019): Fostoria dhimbangunmal, gen. et sp. nov., a new iguanodontian (Dinosauria, Ornithopoda) from the mid-Cretaceous of Lightning Ridge, New South Wales, Australia. J. Vertebr. Paleontol., 4634. 10.1080/02724634.2019.1564757

[3]Bell, P.R., Fanti, F., Hart, L.J., Milan, L.A., Craven, S.J., Brougham, T., & Smith, E. (2019): Revised geology, age, and vertebrate diversity of the dinosaur-bearing Griman Creek Formation (Cenomanian), Lightning Ridge, New South Wales, Australia. Palaeogeogr. Palaeoclimatol. Palaeoecol., 514, 655–671. 10.1016/j.palaeo.2018.11.020


Figure 4 : Opalised bone from the 'hand' or 'foot' of a dinosaur.

Travelog / meeting

Australia :
a great gemological heritage

1/4 Opals from South Australia

Boris Chauviré; June 2023

Map of the State of South Australia, showing the main opal zones mined.

Among opal-producing countries, Australia dominated the market throughout the 20th century. The island-continent is home to around ten areas where opal has been or is still being mined. During May and June 2023, with the help and support of the Gemmological Association of Australia (GAA), Boris Chauviré had the opportunity to observe some of the areas that have produced the exceptional opals that have made this gem’s reputation. The main aim of this trip was to share the scientific expertise acquired on opals with the players in this market, from miners to retailers. The trip also aimed to better constrain and understand Australia’s opal-bearing zones, by sampling the rocks and opals in each area, but also by collecting the knowledge that miners have acquired over time.


Opals were first discovered in Australia in the 19th century, although legends about them existed before that. Some references to this gemstone can be found in the Aboriginal cultures that inhabited this land tens of thousands of years before the arrival of Europeans (up to 65,000 years ago according to recent estimates). These legends vary from tribe to tribe, but they often refer to the rainbow that is said to be trapped in the gem (the rainbow being a very important part of Aboriginal culture). There have been few studies of the place of opals in Aboriginal culture, as their oral nature meant that they could not be passed on after colonisation.

The rediscovery of opals in Australia spanned the whole of the second half of the 19th century and the beginning of the 20th, and it is in the last areas to be discovered that the journey begins. Three main areas stretch along the Stuart Highway, which links Adelaide (capital of the state of South Australia) to Darwin (capital of the Northern Territories). All located in the state of South Australia, they are, from south to north: Andamooka, Coober Pedy (formerly known as the Stuart Range) and Mintabie.

Generally speaking, although numerous models have been proposed to explain the formation of opals in these regions, none of them allows miners to really know where to mine. The prospecting stage is therefore empirical and differs slightly depending on the area, but it primarily consists of looking for “floatters”, pieces of opal found on the surface, without having to dig. To make detection easier, they sometimes use UV lamps at 365 nm (long UV), as these opals fluoresce white to greenish under these lamps. Once an area has been defined, it may be decided to drill for “tracers”, pieces of opal at depth. Then mining begins to extract as much stone as possible, using different methods depending on the operator. In terms of nomenclature, miners use the word “potch” to describe an opal with no play of colour (called common in gemology), and often refer to precious opals (with play of colour) as “with colour” opal.


The last area to be discovered is the southernmost, Andamooka (Figure 1). This small village 600 km north of Adelaide (6h-6h30 drive) is very easy to reach by road, but there is little in the way of entertainment. There is currently only one means of accommodation (the other hotels/motels have all closed), a petrol station and a small mini-market. Most of the old shops that sold opals in the past are now closed, and there are only two places in town where you can see the opals that have emerged from the ground. Yet the area was a major opal producer from its discovery in the 1930s through to its decline from the mid-1970s to the present day. Of the several thousand inhabitants who lived there in the boom years, only 262 remain at the 2021 census[1]. The population is sustained only by the copper and uranium mine at Roxby Downs, just a few dozen minutes from the town.


Figure 1 : Andamooka !

Figure 2 : Opal coating (the small white/blue part to the right of my finger) in a quartzite pebble. This type of association is typical of Andamooka.

Although the town seems to have lost some of its attraction, there are still around 130 claims in operation in Andamooka, according to the local office of the South Australian government’s Department for Energy and Mining. A “claim” is a parcel of land (ranging from 50x50m to 100x200m) where the holder of a permit can prospect, exploit and sell the production from his parcel. In fact, although the population has declined sharply, it would appear that the town is still mining opals.

Andamooka opals are renowned for their stability, which is said to be far superior to that of other mined areas. One of Andamooka’s special features is the so-called “Painted Ladies”, opal veneers in the cracks of banded quartzite pebbles found in a white/grey to slightly reddish argillite (Figure 2). This argillite also contains horizontal and vertical veins of gypsum. Opals are also found in veins directly in the argillite, in the form of horizontal or vertical veins (resembling fissures).

Mining here can be mechanised, but it generally seems to be manual. The excavator’s role is to uncover the levels, and the new outcrop thus revealed is inspected by hand for potential. Miners sometimes use a long UV lamp to reveal the presence of opal, an operation that is carried out at night (Figure 3). A large collection of opals, mainly from South Australian mines, is on display at the Andamooka Dukes Bottlehouse Motel. If you want to discover this village, this collection is definitely a must-see.


Figure 3 : Outcrop at night under a UV lamp, showing blue/white opal patches.

Coober Pedy

Coober Pedy is one of the best-known names for Australian opals, often even referred to as the opal capital of the world (Figure 4). Easily accessible via the Stuart Highway, nine to nine and half hour drive from Adelaide, this town of 1,566 inhabitants (as at the 2021 census[1]) is one of Australia’s largest and most active opal producers. The dozen or so opal shops (from raw opal to jewellery pieces) on the main street, and the several opal museums providing information on current and past opal mining methods, bear witness to the central role played by the gem in the life of the town. Old mines, or simple hollows in the rock, have often been converted into accommodation, providing an unusual and typical way to discover the town (and avoiding the intense summer heat).

Although the number of opal miners has fallen since the boom of the 1980s, there are still more than 400 declared claims throughout the Coober Pedy area. The mined area extends over several dozen kilometres, and each zone has a specific name. The names are often transparent about their meaning, for example Five Miles or Fourteen Miles are simply 5 and 14 miles from the town, or the Emu Flat which is a place where emus were commonly observed.


Figure 4 : On arrival in the town: it's obvious that we're in an opal town...

Figure 5 : Fossil of an opalised bivalve, with blue to violet plays of colour.

Coober Pedy opals are generally white to colourless, and opalised fossils are regularly found (Figure 5). These fossils are generally bivalve (mussel class) or brachiopod (bivalve-like cousin) shells, or even belemnites (conical bones from an ancient cuttlefish cousin). Although rare, opalised dinosaur fossils have been discovered, such as Eric, an opalised pleiosaur now on display at the Australia Museum in Sydney.

The opals of Coober Pedy can display a kind of stratification, sometimes alternating between common and precious opals. Opals are often found in the form of horizontal veins in a white to red argillite (called “sandstone” by most miners), in levels that miners identify by the presence of red to brown layers. Vertical fissures are rarer, but in a few cases they can produce large quantities of high-quality opal. They look for evidence of tectonic activity, such as faults or vertical fissures, which they believe allow the finest opals to be found in the levels.

Mining is mechanised, both above ground and underground. The rock is extracted by excavators (shovels) in the open air, or smaller models in underground galleries. In the case of underground mining, the rock is brought up by machines that have become a symbol of Australian opal mining: blowers. These trucks have a powerful pump that sucks (it would be more accurate to say “suckers” rather than “blowers”; Figure 6). The rock is then sorted according to grain size, without the addition of water, before being sorted by hand under long UV lamps to detect opals. Although this type of information must be treated with caution, the sorting method means that we can expect the vast majority of Coober Pedy opals arriving on the market to fluoresce under long UV light.

In parallel with these operations, a few people use a UV lamp to look for opals in areas that were previously mined or not yet prospected. This operation, known as “noodling”, is also a tourist attraction in dedicated areas. Some report that good quality opals can easily be found in specific areas. For opal enthusiasts, Coober Pedy is a must for discovering Australia’s opal deposits.


Mintabie is a small village about 350 km north of Coober Pedy, west of the Stuart Highway. This area was considered to provide South Australia’s finest opals during the boom of the 1980s. Although the name is less famous than Coober Pedy, Mintabie is said to have been an opal producer on a par with the latter in the 1980s and 1990s, with several hundred claims also declared. However, the village was closed down by the South Australian government in 2019, due to the fact that many of its residents were illegally housed there. Rumour has it that the closure of the village was due to an upsurge in violence and trafficking of all kinds. Today, only around fifteen claims are registered in the area, access is complex and few minors stay there permanently.


Figure 6 : Old blowers, with the characteristic shape of a lorry with an arm blowing the rock deep into the earth.


The "Voi Gemstone Addition Center", Kenya

Lauriane Pinsault; March 2023

David Irungun, the regional mining officer of the Voi Gemstone Value Addition Center

In-between mine visits around the very gemstone-rich region of Taita-Taveta, the Kenyan district, at the west of Mombasa, that contain the Tsavo National Park. There, we had the opportunity to meet David Irungu, the regional mining officer of the Voi Gemstone Value Addition Center (referred hereby as the “center”). David’s role in the center includes multiple tasks, from disputes resolution, mines’ inspections, and compliance to advisory and liaison services between investors and mines owners. David presented us this new center in Voi and its purpose. He also gave us many information about the gemstone mining sector and its regulations in Kenya.

The Voi Gemstone Value Addition Center is a National Government Building built in 2015. The center was not officially opened yet at the time of our visit, its opening, planned for the first quarter of 2023, has been postponed since several years awaiting for the President to commission it and is. This one-of-a-kind center in Kenya is highly awaited by the miners, as its primarily focus is the promotion and support of the artisanal and small-scales miners (ASM). Indeed, the center comprises of 5 main facilities:

  • Trading booths, available for rental, where buying and selling between miners and dealers can happen in a secured environment.
  • A laboratory, with gemstone identification equipment, as well as engraving and cutting planner machines.
  • A cutting and polishing area, for both training and services.
  • A safe room, to reduce the product movements outside of the building.
  • Conferences rooms for meetings and trainings.

The vision of the center is primarily to provide a safe and legal environment for the trading of gemstones in Kenya. The buyers will be ensured of the legality of the gemstone’s extraction as the miners who will access the center will have to be declared and have permits. Trading within the building will avoid the smuggling of the gemstones and ensure a better valuation of the product. All sealing and exports processes can be done directly in the center, which is an important benefit as currently these processes can only be done in Nairobi. Another objective of the center with its cutting facility is to add value within the country and before the exports of most of the gemstones produced.

One of David’s job is to maintain compliance of the mines operating in the region. The mining legal framework in every country is dictated by the mining law. Understanding the basic of a mining law in a country is essential if you want to be able to assess and ask the right questions about the formality and legality of a mineral product. In Kenya, the mining law has been recently updated called the “mining act of 2016” and is in use since 2017, from its former version of 1940. However, work on this law is still ongoing, especially to integrate the ASM. Indeed, the documents required to obtain permits, as well as the size of the mining area, should not be the same for a large-scale operation and an ASM operations. However, David raised the issue of delimiting the type of operations: when do an artisanal mine becomes small-scale, semi-industrial, or industrial? One cannot base this differentiation on the number of persons nor the machinery, thus several criterium should be considered as well as the evolution of the mine. This shows the complexity that many countries face when regulating the mining sector, and particularly the extraction of products like gold and gemstones which has been widely small scale and informal.


The Voi Gemstone Value Addition Center building

Meeting with artisanal miners in Kasigau

In the Kenyan Mining law, two types of licenses exist: the prospecting license and the mining license. The first one aims for the exploration of a land; it lasts for 5 years and is cheaper than the mining license. A renewal is possible but the concession has to be reduced considering that exploration work should have given results and restricted the interesting area. Logically, this type of license should ultimately lead to the application of a mining license, which last for 25 years (also renewable). In fact, the number of mining license is very little, and a majority of the gemstones mines operates under a prospecting license. Selling gemstones from a prospecting license is legal, as long as they are declared to the taxes and customs.

Before applying for a license, a miner should identify an area with GPS coordinates and verify on the cadaster that this area is free of license. The process of application requires a number of documents to be submitted: some are common to both type of license (criminal records, taxes compliance, identity papers, etc), and some are expected to be more detailed from the mining license (preliminary study report, environmental impact assessment, work program, budget, life-of-mine, mine closure and rehabilitation, etc.). Considering the costs and the paperwork related to these permits, artisanal miners are encouraged to create communities and cooperatives. The center also aims to help them in this process, and hope to be allow to deliver them licenses directly in Voi instead of Nairobi.

There is also a will to change the current regulation on the dealer license in order to avoid the illegal trade and exports, which is unfortunately important in Kenya. Indeed, the current dealer license process is cumbersome (it can take up to 8 months to get) and once delivered the license is valid for only one year with an expiry date at the 31st of December, regardless of the date of deliverance. The objective would be to extend the validity of this license to encourage its application. Dealer’s license is accessible to both Kenyan citizens and foreigners as long as they have an office in Kenya with safety facilities.

We greatly thank David Irungu and his colleagues from the center for their warm welcome and their time. We can’t wait to come back and see the center in operation!


Le "laboratory" of the Voi Gemstone Value Addition Center

Simplified map of the most important Taita-Taveta gem deposits.

Further readings :

Note on the gemstone mining history of Taita-Taiveta:

The Taita-Taveta region comprises of 4 counties, namely Taita, Taveta, Mwatate and Voi. The region has a rich history of colored gemstone mining since 1967 when Tsavorite was discovered by Campbell Bridge[1] (deposit that will be exploited later under the name of Scorpion mine). A few years later, rubies were discovered nearby, at the deposit that became the John Saul Mine in 1973[2]. Other gemstones are also mined in the region, notably green and yellow tourmaline[3]. The Taita-Taveta province is considered to be one of the richest area in Kenya for mining both gemstones and industrial minerals. A 2014 study estimates that more than 80% of Kenya’s earning from the gemstone industry in 2003 was attributed to the ASM sector[4]


[1] Bridges, B., & Walker, J. (2014). The Discoverer of Tsavorite—Campbell Bridges—and His Scorpion Mine. Journal of Gemmology, 34(3).

[2] Emmett, J.L., Prairie, B., (1999). An update on the John Saul ruby mine. Gem News. Gems & Gemology. Winter 1999

[3] Simonet, C. (2000). Geology of the Yellow mine (Taita-Taveta District, Kenya) and other yellow tourmaline deposits in East Africa. JOURNAL OF GEMMOLOGY-LONDON-, 27(1), 11-29.

[4] Anyona, S., & Rop, B. K. (2022, March). The character and profile of artisanal and small-scale gemstone mining community in Taita Taveta county, Kenya. In Proceedings of the Sustainable Research and Innovation Conference (pp. 109-125).

Travelog / school

The vocational training center of Arusha, Tanzania

Lauriane Pinsault; March 2023

Students at the VTC (Vocational Training Center) in Arusha

Our second stop in Tanzania brings us to Arusha, an important place in the country for colored gemstones trading, thanks to the famous TanzaniteOne mine (the only known tanzanite mine in the world), located nearby in Merelani Hills


We were welcomes at the Vocational Training Center (VTC) of Arusha, a gemmology and faceting school, to visit their facilities and discuss about the gemstone industry within the country. 

The VTC exists since 2000 and has trained more than 800 students since its opening, which represents, according to the director of the school, more than 97% of the certified cutters in the country. The cursus includes gemstones identification, grading and sorting, but mainly focused on cutting lessons, over a 6-month program. The students are trained on both local and international cuts. Both types of cuts are done following indexes for angles between facets, but crudely, the difference relies on the retention of the weight. Locally, the cutters tend to retain more weight because they feel they get a better price (as gemstones are bought in $/ct). However, these local cuts are very often recut to integrate the international market, who demand higher quality of cut over weight (perfect symmetry, optimized proportion for light refraction and dispersion, etc). The students start their cutting training on marbles, before moving to natural gemstones.


Facetting work in progress on marbles

Fixing the gemstone with dop

Facetting machine

Student working on the preparation of the gemstone table, before facetting

Lauriane discussing with a student about fecetting methods

The number of students per section varies a lot, mainly depending on the economical and political situation. Since the change in politic regime in 2015, the school observed a significant decrease in students’ registrations. They also fundamentally rely on the industry, for example the closure of TanzaniteOne mine was a major hit it was the main hiring company for many certified students. The current situation is difficult for the school, particularly with the impact of Covid and the Ukranian conflict, due to the lack of work opportunities after graduation. The director stressed that the school is still opened nowadays thanks to the support of the NGO GemLegacy who played an important role in the existence of the center for several years now. 

Conversation around the gemstone sector highlighted the opportunities and challenges in the country. The discovery and development of tanzanite mining in Merelani led to a strong social and economic growth of the region, but also of the entire Tanzanian gemstone industry. According to the director of the VTC, the major current brakes the sector are mostly related to the lack of governance and poor regulations. The country and people would benefit more of the true value of their gemstones if they were cut within the country, in line with the law on tanzanite that officially request all tanzanite’s above 2g to be cut before the export. In reality this regulation is loosely enforced and tends to encourage smuggling more than in-country beneficiation. The director argues that they do have trained labor force in the country to ensure the beneficiation process as many students have been graduated from his school in the past 23 years, and they could absorb more if the need was there. Another example of regulations that could promote the local skills, gemstones and sector would be to enforce the gem master dealers in the country to have cutting machines*.


The school director, Lauriane and the school teacher

We are very thankful to GemLegacy for
putting us in contact with the VTC, and a big thanks to the VTC staff and
students for sharing their knowledge and experience. 

*The articles on this blog relate the opinion of industry actors, and therefore should not be considered as GeoGems point of view, which remains neutral. It is for every reader to learn, think, reflect, and debate on the raised subjects.
Travelog / Mining

Artisanal Mining in Morogoro, Tanzania

Lauriane Pinsault; January 2023

Visit of a mining site, with the chairman of the Matombo miner association, a women artisanal miner, and Alpha from PDI tanzania

In January 2023, GeoGems had the chance to visit an artisanal ruby mining site in Tanzania.

A massive thanks to Alpha Ntayomba, executive director of Population and Development Initiative (PDI) in Tanzania, who organised this visit and welcomed us in Morogoro. PDI is an NGO, originally based in Kigoma (west of Tanzania, on the edge of Tanganyika lake), now installing an office in Morogoro. Morogoro, and the whole Uluguru mountains, are well renowned for gemstones, including corundum, spinels, amethyst and garnets. In this gem-rich area, PDI promotes responsible mining amongst ASM (Artisanal and Small scale Mining) communities, on various commodities from gold to gemstones.

We were also accompanied to the mining site by the chairman of the Matombo Miner Association, himself a miner in the area for the past 30 years.

Exploitations are all open-pits, 5 to 10 m deep, making the extraction pretty easy for artisanal exploitation. However, no safety equipment is in use (the miners are even operating bare foots), and many old pits were left abandoned. The miners told us that the size of the ruby deposit was about 1km², with around 100 artisanal miners working on the different concessions. Considering the wide gem-rich area, the number of miners operating around is much likely higher.

As the deposit is on privately owned land, the miners pay an exploitation fee to the landowner and operate legally with a licence to mine. Miners are generally organised in groups of 3 to 10 people, with dedicated roles and a leadership system. However, no formal contracts exist between them: they share the revenues from the sales based on verbal agreement. Very few women are involved, and when they are, they mostly take care of the food and logistics. Sometimes, the landowner is also a miner himself, in which case he gets the “rent” for the land, plus the share of revenue from the sales. The miners admitted that this informal organisation on the division of the revenues could sometimes lead to conflicts. 


Artisanal miners working in Matombo

Pits and bags of ores at the artisanal mining site

The mine visited was located in Matombo, and produces mostly red corundum (rubies), pink spinel and green tourmaline. The deposit is secondary, with the gemstones found in a layer of red soil. Big crystals of quartz and schorl were also part of the ore. The miners explained that they were following a layer composed of big pebbles of quartz and aggregates of minerals, which they consider being an indicator for the presence of rubies and spinels. No gemstones were directly found on site (from the pits or the ore) during our visit, but quickly the miners showed us some of their production. Notably, their best “rubies” was a bring fluorescent pink spinel (with a nice and clear octahedron shape). Indeed, miners are doing the distinction between rubies and spinels based on the colour only, which leads to errors in identification.

The production is variable, especially with the season as the mining activities are more important during the dry season than the rainy season. This is because most of the miners have another occupation, often farming. From the mine visited, about 10kg of gemstones was produced per month (unclear if it is comprising all gemstones or only corundum). The rubies that were showed to us were all of medium to low quality, showing good colour but bad clarity. 

Once produced, the gemstones are roughly graded into different quality categories before sales. For the past 2 to 3 years, the Tanzanian government has opened markets and auction places, in order to encourage miners and buyers to declare their production and sales, and thus to pay the related taxes. In Matombo, the “auctions” take place twice a week, and bring together hundreds of miners for about ten big buyers. Buyers are often from other countries like Kenya. Although they see this selling place as a good opportunity for them, the miners admitted that what they are looking for is quick profits, so they continue to sell directly to buyers if they are approached outside of the auction time and place. The revenues from the mine visited are between 800 000 TSH (344 USD) and 3 000 000 TSH (1 290 USD) per month. Considering 10kg of gemstones produced per month, that an average sale around 0,02 ct/$. Also considering that 6 miners were operating at this site, is gives an average wage of 500 000 TSH (215 USD), corresponding to the minimum wage for mining companies in Tanzania[1].


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Production from the Matombo mining area, comprising of spinels, rubies and green tourmaline

Pit and nature surrounding in Matombo

This visit represented well the complexity of the ASM sector, and notably for the extraction of gemstones. First, the miners are operating legally, and make a living out of the sales of their production. They organise as they consider is the best and have been operating this way for many years. However, the lack of formal arrangement on the share of revenue, as well as safety standards, which could lead to human rights abuses and major injuries. The will for quick profits, combine with the mistake in gemstone identification and quality, is also a threat because it leaves space for the buyers to purchase the production at lower value than it is worth, especially when buying outside of the government marketplaces. Addressing the challenges of the sector to efficiently implement responsible mining in such context entails for all actors (miners, buyers, governments), to agree on a common strategy and global vision, and for each to find a benefit in it, which is yet to be done.

Note on history:

Morogoro region is vast, and many gemstone deposits are found there, with, amongst the most famous ones, Kitonga, Lukande, Matombo and Mahenge. Rubies from Morogoro are known since the 1970s, but the gemstone arrived in the market in the 1980s[1], peak of production happen between the mid-1980 and the mid-1990s[2]. The production in 1992 was estimated to be around 200kg per month, with quality being again mostly cabochon and carving grade[3].

[1] Hänni, H. A., & Schmetzer, K. (1991). New rubies from the Morogoro area, Tanzania. Gems & Gemology, 27(3), 156-167.

[2] Hughes, R. (2008) Gem Hunting in Mahenge & Tunduru.

[3] Schwarz, D., Pardieu, V., Saul, J. M., Schmetzer, K., Laurs, B. M., Giuliani, G., … & Ohnenstetter, D. (2008). Rubies and sapphires from Winza, central Tanzania. Gems & Gemology, 44(4).


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