Diamonds are precious stones formed at the greatest depths of the Earth, approximately 150 – 200 km, yet they are still not as challenging to extract as emeralds.
Diamonds and emeralds are two of the most sought-after and valuable gemstones. In terms of known reserves, emeralds are rarer. There are 49 emerald mines, according to a 2019 review published in the journal Minerals. In contrast, there are approximately 1,000 diamond-bearing structures, although only 82 diamond mines are currently operational, as reported in a 2022 study in the journal Reviews in Mineralogy and Geochemistry. However, it is challenging to compare the quantity of diamonds with other gemstones due to the more developed diamond industry.
A diamond and emerald necklace that once belonged to actress Elizabeth Taylor was displayed at the Victoria and Albert Museum in London in 2014. (Photo: Rob Stothard/Stringer)
Each year, 100 – 150 million carats, equivalent to around 20 – 30 tons of diamonds, are produced worldwide, according to the Natural Resources Canada agency. Meanwhile, based on market research data from 2022 by the mining company Gemfields (UK), approximately 6 – 9 tons of emeralds were produced in 2015 from major producing countries (Colombia, Zambia, Ethiopia, Madagascar, Brazil).
According to Gemfields, tracking the global output of any gemstone other than diamonds is very challenging due to the scattered mines worldwide, primarily operated by small companies. However, these figures do not fully reflect the geological story. Both diamonds and emeralds form through complex processes.
“For both of these, you need a unique set of geological conditions for everything to come together just right“, shared Evan Smith, a senior research scientist at the Gemological Institute of America.
For diamonds, these conditions originate deep within the mantle, the middle layer of the Earth. According to a study published in the journal Gems & Gemology in 2018, diamonds form at depths of 150 – 200 km underground, making them the deepest-forming gemstones on the planet.
Diamonds form as single carbon crystals. Geologists believe this occurs when there is a change in pressure, temperature, or a chemical reaction that cools the molten mantle rock containing carbon, Smith explained.
For diamonds to reach depths that can be mined, a rare volcanic eruption is required, known as kimberlite, which forms from magma at depths of about 170 – 300 km underground. On its way to the surface, kimberlite can pass through an area containing diamonds and carry them up.
Diamonds are fairly evenly distributed within kimberlite structures, making large-scale extraction feasible, Smith explained. However, the same cannot be done with emeralds.
Emeralds form in more complex geological structures, suitable for small-scale, manual mining. Emeralds are the green variety of the mineral beryl, obtaining their color from the presence of chromium and/or vanadium. Beryllium, the primary element in beryl, is concentrated in the magma of the continental crust. Chromium and vanadium are more prevalent in the upper continental crust. For emeralds to form, these distinct geological environments must meet.
“You need two factors to react to create emeralds,” shared Chris Tacker, a geological researcher at the North Carolina Museum of Natural Sciences. This often occurs when beryllium or beryl-containing rocks come into contact with sedimentary rocks like limestone or shale, or when magma flows through surrounding rock environments and absorbs chromium. For this reason, emeralds are often found in “collision zones” like mountains, where tectonic plates collide and various geological environments meet.
While the geological conditions that create diamonds and emeralds are both unique, in terms of accessibility for humans, emeralds are certainly rarer.
