What Country Do My Diamonds and Other Gemstones Come From?
April 24, 2020
“Since 1931 (GIA’s founding), we have shared everything we have learned with you.”
This quote from Richard T. Liddicoat, GIA’s legendary second president, is how Dr James Shigley began his recent lecture, “Gemstone Country of Origin Reporting”.
“It is the best short description of why GIA is here,” said Shigley, who is GIA’s distinguished research fellow and holds a Ph.D. in geology from Stanford University. Shigley proceeded to share everything (or many of the things) he’s learned about gemstone origin in his 37 years of working in GIA’s research department. He focused most of his presentation on coloured stone origin identification, which is detailed in a special Winter 2019 issue of Gems & Gemology (G&G) on country of origin.
“Country of origin reporting [for coloured stones] is probably the most difficult challenge we have in the lab for identifications purposes,” Shigley said.
GIA researchers are uniquely able to offer insight into coloured gem origin, he explained, because of the sheer volume of stones they see in the lab and in the field. In the past decade, GIA field researchers have gone on 95 field expeditions to 21 countries and collected more than 22,000 samples totalling more than 1 million carats. GIA also has 60 researchers on staff, including more than 20 with doctoral degrees in fields such as geology, chemistry and material science.
The knowledge gained from these field expeditions is part of the “foundation” of the information GIA can provide to the gem trade in its coloured stone report service, Shigley said. The GIA Coloured Stone Identification and Origin Report has been around for decades, but the GIA Diamond Origin Report is relatively new.
How Does GIA Determine Where Coloured Gems are From?
“It’s important to recognise that a country of origin report is an expert opinion. We [often] weren’t there when it [the gemstone] was found,” Shigley said. “It is an expert opinion based on examination of the sample that is presented to us.”
The assumption is that stones from different places should have different gemmological properties he said, but it “doesn’t always pan out that way”.
Shigley reviewed some of the challenges of country of origin reporting for coloured gemstones:
The geology of the gem deposit is often not well known and many alluvial occurrences have an uncertain source (“We don’t know where the original host rock is located,” he said. “it could be miles and miles away.”)
Access to the deposit may be difficult.
Gem deposits do not stop at country borders.
Deposits in different countries can produce very similar material (such as sapphires from Madagascar, Kashmir and Sri Lanka).
Different deposits can be found in the same country.
“What these challenges show,” Shigley said, “is that the geology determines the gemmological properties — the inclusions, the chemistry and all of the other properties of the gem material.”
Country or geographical origin reporting began in the 1950s when the famous Swiss gemmologist Eduard Gübelin started to provide letters about where the stones his company was selling came from, Shigley said. Gübelin also wrote a series of articles for G&G on how inclusions can help to determine where coloured stones come from.
Building on what researchers have learned and documented in the past, GIA created a field gemmology programme a decade ago to “go to where the gems are,” Shigley said. They are collecting samples to build a reliable database, videotaping and photographing the area, and interviewing miners to get a complete picture of what’s going on in that particular place and at that particular time. He said this programme is the foundation of GIA’s Coloured Stone Country of Origin Reports, and it provides valuable information for GIA education courses.
While coloured gemstones continue to be found in Australia, Brazil and Columbia, in many cases today they are found in two regions of the world. The first is the arch of countries between the Indian subcontinent and Asia (Iran, Pakistan, Afghanistan, northern India, Myanmar, Cambodia, Vietnam and Thailand) that represent the collision zone between India and Asia — this collision zone produced the metamorphic and magmatic conditions necessary to form gem deposits. The second region represented is Eastern Africa (Ethiopia, Somalia, Kenya, Tanzania, Madagascar, Mozambique), as well as Sri Lanka and southern India — another continental collision zone with the right geological conditions to produce gem deposits.
GIA field gemmologists travel to these countries to collect gem specimens for research. These specimens are classified according to how close to the source they are when they are collected:
Type A ‒ collected on-site by a GIA gemmologist
Type B ‒ the gemmologist witnesses the samples being mined
Type C ‒ samples are purchased from a miner at the mining site
Type D ‒ samples are purchased from a miner but not on-site
Type E ‒ samples are purchased from a secondary source (not the miner) close to the mine
Type F ‒ samples are purchased from a secondary source on the international market
Most of the samples GIA collects are Type D or E, supported by types A, B and C when available. These samples are taken back to the lab so that researchers can study their colour, fluorescence, inclusions, growth zoning, chemical composition, spectra (visible and infrared), Raman spectroscopy and photoluminescence. These stones are also photographed, often at 100x magnification, to record their inclusions and other visual features. The data collected lets scientists determine the cause of colour in the gem material at hand, which helps to determine origin or to classify gemstones into different types.
The instruments needed to collect all of this data, such as the scanning electron microscope and the laser-ablation mass spectrometer, cost anywhere from $100,000 (£80,000) to $1 million (£800,000) each. Some of these instruments are able to detect very tiny quantities of trace elements in the quantity of parts per billion (PPB), and can pick up elements that are unique to certain countries of the world. The greatest challenge in collecting data on gemstones is using non-destructive ways to analyse them.
Another challenge to gemstone origin determination is that countries are continually being added to the list as gemstones are discovered at new locales, so GIA field researchers are always on the march to document more gemstones. Shigley used ruby as an example of how the discovery of new deposits has increased over the years: in 1950 there were eight known ruby sources in the world, today there are 30.
“They don’t necessarily produce the best quality of material, but material from all of these deposits are in the market and may show up here for an origin report,” he said. “The challenge is the growing number of localities with very different geology — and sometimes with very similar geology.”
“The database is accessible in GIA’s identification laboratories for comparison with client stones for country of origin services. Each expedition expands the database and improves the reliability of the reference collection and GIA’s laboratory services.”
Can GIA Figure Out Where a Diamond is From?
Shigley also discussed how determining coloured stone country of origin differs from determining country of origin for diamonds, which is nearly impossible, because once a diamond is cut, there are no distinctive features to determine where it came from.
“We cannot tell where a diamond comes from based on the diamond itself,” Shigley said.
Certain mines, however, are associated with a certain size or quality of diamond, e.g. the Cullinan Mine in South Africa, which is renowned for having produced several legendary large, high-clarity diamonds, including the Cullinan, the largest diamond rough ever found. The Argyle Mine in Australia has been the world’s primary producer of pink diamonds for decades.
Shigley outlined the main reasons why it is impossible to determine the geographical origins of diamond based on gemmological and scientific examination.
Where they form: Diamonds form deep in the Earth, where conditions are more homogenous. Also, there aren’t any distinctive mineral inclusions associated with any particular location.
Diamond structure, chemistry and analytical challenges: Diamonds are made up of carbon and sometimes a small amount of nitrogen and boron, which are next to each other in the periodic table, Shigley said, so the atoms are about the same size and can easily substitute for one another in the diamond structure.
“Diamond is a very close-packed tetrahedral arrangements of carbon atoms that are held together by very strong short, covalent bonds,” he said. “It is hard to get other trace elements into the diamond structure in very much quantity. [If they are there] they are very trace amounts in the parts per billion level.”
Additionally, analysis of trace elements in diamonds requires sophisticated analytical equipment and a method that may destroy part of the diamond sample. Spot analysis can be done using Secondary Ion Mass Spectrometry (SIMS), but this is “probably a million-dollar piece of equipment” usually only found at universities — GIA does not have one, Shigley said
Weathering: Some diamond deposits are secondary, where the diamond is recovered from a river or sediment by panning. Diamonds are brought to the Earth’s surface by an explosive eruption that forms a volcanic pipe filled with diamond-bearing igneous rock known as kimberlite. Kimberlite weathers quickly, releasing the diamonds and they move downhill, taken either by gravity or water, and are then carried by river systems downstream — possibly hundreds of miles away — or incorporated into sedimentary rock.
“The river takes them many miles away from their original pipe location, so we don’t even know where the pipe was,” Shigley said. “And of course, the river crosses many countries. In South Africa, it [the Orange river] transports them all the way to the Atlantic Ocean.”
Lack of a distinctive surface appearance on rough diamonds: Experienced diamond sorters at DeBeers might be able to tell which company mine a rough diamond came from based on its surface features, but this isn’t an exact art and the stones are unrecognisable once surface characteristics are removed in the gem cutting process.
Shigley said the real problem of diamond origin is: Where are you going to get diamonds to study to develop your criteria for country of origin identification?
“You would need a representative sample of diamonds from all of the mines in the world and all of the secondary deposits in the world. And what’s a representative sample — is it 3 or 300 diamonds [from each location]?” he said. Additionally, once you have representative samples, they would have to undergo destructive testing.
“There is no database of rough diamonds available to anyone to tell where they are from and I don’t know of any way, scientifically, to tell where a polished diamond comes from,” he said. “The database of samples, if it existed, would provide a source of information to try and develop ideas for country of origin determination for diamonds,” he said, adding that the lack of diamonds from secondary alluvial deposits “is a particular problem because of the lack of organised mining efforts and the random finding of diamonds”.
It’s in the leap from rough to polished that GIA bridges the gap. GIA works with diamond mining companies in major diamond-producing countries such as South Africa, Russia, Canada, Namibia, Lesotho and Australia to offer the GIA Diamond Origin Report Programme to the gem trade.
“It’s more of a matching service,” Shigley said. GIA takes a rough diamond that comes in a sealed parcel from a client or programme participant with its required origin documentation. GIA characterises it so that it is later able to match it to a cut stone submitted for the origin service. The country of origin information confirmed in the report comes directly from the mine.
‘We are saying [on the report] that this is where it is from and we can definitively match it with the original rough diamond,” Shigley said.
GIA matches the gems to their original rough according to their size and colour, measurements, gemmological observations, absorption and luminescence spectroscopy, fluorescence imaging and information in the GIA database. Each GIA Diamond Origin Report also contains a 4Cs quality analysis in addition to a statement of origin.
GIA has issued nearly 20,000 diamond origin reports.
Amanda J. Luke, a senior communications manager is the editor of the GIA Insider and an editor and writer at GIA for 19 years.