Not All That Glitters is Gold — Sometimes it is Mozambican Rubies

Wim Vertriest, supervisor of GIA field gemmology, presented his lecture "A Decade of Mozambican Rubies" on 30 Jan 2020 as part of the GIA Guest Lecture Series. Video Duration: 1:21:10

There was something striking about the talk, “A Decade of Mozambican Rubies”, that Wim Vertriest, head of GIA field gemmology, gave at GIA in Carlsbad recently. It’s only in the past 15 years that there has been intense consumer scrutiny of gemstone origins. Previously, unless a stone was from a legendary locale, such as Kashmir for sapphires, origin was largely ignored.

Vertriest’s talk, however, dived deep into rubies from a new and lesser known locale — Mozambique — focusing on their mining history, characteristics and market demand. Throw in some tips on field gemmology from GIA’s “viking” gemmologist, Vertriest, and the talk was as good as gold.

A group of seven rubies.
These rubies (1.07-4.62 ct) are from Northern Mozambique. Photo by Robert Weldon/ GIA. Courtesy of Tommy Wu, Shire Trading Ltd., Hong Kong.

Mozambican Ruby Discovery

Mozambican rubies, unheard of a decade ago, have become the most common ruby in the international marketplace since their discovery in 2008. Mozambican rubies now make up a significant part of the rubies sold at major trade shows.

A large group of miners work around small digs.
A group of garimpeiros, or mineral prospectors, mining in the bush surrounding Montepuez. Photo by Vincent Pardieu/GIA.

Timeline from Discovery to Present

2008 ‒ The first confirmed ruby is found at the Niassa Reserve, an area set apart for wildlife such as lions and elephants. Its protected status doesn’t stop artisanal miners from flocking to the site, however. Mining virtually ends in summer 2009 when water sources dry up and miners are forced to leave.

2009 ‒ Rubies are discovered next to a major road near the town of Montepuez. Tens of thousands of artisanal miners flock to the site. Within a year, international traders start acquiring rubies in the towns near the mines. Stones are transported to cutting and trading centres such as Bangkok, making Montepuez the dominant source of rubies for the Thai ruby trade.

2014 ‒ Mwiriti Limitada, which owns a significant number of mining licences around Montepuez, partners with the natural resource company Gemfields to form MRM. The first rubies are exported following government-approved processes.

2020 ‒ In less than a decade, ruby mining has transformed from 100 per cent artisanal to largely formalised. But even though several companies have set up large-scale ruby mining operations in Mozambique, there remain many artisanal miners.

A pile of rough of rubies with a coin for perspective.
Maninge Nice-type rubies (here, up to 17 mm) are typically a deep red with strong fluorescence but also flat and highly-included. Photo by Vincent Pardieu/GIA.

Mozambican Ruby Quality

Mozambique produces two main types of rubies: Maninge Nice (known as Bor Daeng in Thai) and Mugloto (Bor Som in Thai). The names of these terms come from the names of the most productive mines in the Montepuez area.

Maninge Nice rubies have brilliant colour, intense saturation and strong fluorescence. But they also tend to be flat in shape and heavily fractured, yielding smaller rubies when cut. Fractured stones are treated through flux healing to improve their appearance and durability. This process entails heating the stones in the presence of borax, which allows the fractures to heal.

Mugloto rubies are bulkier in shape and have fewer fractures than Maninge Nice rubies. They tend to have darker tones and weaker fluorescence, however. Mugloto stones sometimes require heat treatment to remove blue overtones and give the stones livelier colour. Detecting this low temperature treatment is challenging and often requires advanced instruments.

An oval-shaped mineral inclusion in a ruby.
Amphiboles are common mineral inclusions in Mozambican rubies, Vertriest explained during his presentation. Photomicrograph field of view 1.32 mm. Photo by Jonathan Muyal/GIA.

GIA in Mozambique

Vertriest’s expertise in rubies comes from years in the field with GIA, collecting research samples in Africa, Asia and Europe. Purchasing gems near their production site is the most foolproof way of ensuring that the stones GIA studies are actually from that locale. According to Vertriest, “if you don’t go, you don’t know.”

The most reliable samples are Type A, which are samples mined directly by the gemmologist.“I go to the mine, hit a rock, and a 10-carat ruby comes out,” Vertriest said.

The other types of classification beyond that are qualified by how the gemmologist collects them:

  • 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 that GIA collects are Type D or E, supported by types A, B and C when available. The research carried out on these gemstones supports GIA’s coloured stone identification and origin reports.



Two men sort through gem gravel on site.
Aaron Palke, senior research scientist at GIA (left), and Vertriest sort through gem gravel in Mogok, Myanmar, in December 2018. Photo by Kevin Schumacher/GIA.

How to Become a Field Gemmologist

Vertriest has a master's degree in geology with a focus in geodynamics and geofluids, a Graduate Gemologist degree from GIA and a diploma in gemmology from the Gemmological Association of Great Britain.

When asked by a student which degree is the most useful, however, Vertriest answered “common sense”.

“Field gemmology isn’t a trade you just jump into,” he said. “It’s a trade that gemmologists grow into through extensive travelling, asking the right questions and working on a research team or as a gem grader. An advanced degree in geology, chemistry or physics is also a must, since field gemmologists are part of GIA’s research department.”

Vertriest’s tools of the trade include a loupe (indispensable, he said) and a gem torch, although he admits a normal torch or even a phone light might work just as well. Having a reliable source of light helps him determine the quality of a stone.

“Traders often sell rubies under pink umbrellas and sapphires under blue roofing; these conditions really enhance the appearance of stones and can make them look better than they actually are,” he said. “Having a torch also helps when examining gems in dim locations or when it’s dark.”

When asked why he works at GIA, Vertriest answered that working for GIA opens many doors. It allows him to go to large-scale mines and artisanal mining sites as well as gem trading offices to study rubies and other gemstones.

“When I go, it’s not, ‘Hi, Wim here.’ It’s ‘Hi, GIA here.’ Once I lose that badge, half the doors close,” he said.

GIA is an incredible resource, he said. GIA’s lab and research departments host some of the field’s greatest researchers who are engaged in some of the most pressing gem issues of the time. In other sectors, field researchers have to rely on external analytical services and wait months for data. Because GIA has its own analytical department, however, Vertriest can request a complicated analysis in the morning and get results after lunch.

The gem trade is exciting when working with GIA, Vertriest said, but prospecting on your own can be “an incredible gamble”.

Phoebe Shang, a senior writer at GIA, is a Graduate Gemologist.