Which is rarer, diamonds or emeralds?

Diamonds and emeralds are two of the most popular and expensive gemstones. In terms of total known reserves, emeralds are rarer. There are 49 emerald mines, according to a 2019 review in the magazine Minerals in 2019. Meanwhile, there are about 1,000 rock structures containing diamonds, although there are only 82 active diamond mines, according to research in the journal Reviews in Mineralogy and Geochemistry 2022. However, it is difficult to compare the number of diamonds with other gemstones because the diamond industry is more developed.

Each year, 100 – 150 million carats, equivalent to about 20 – 30 tons, of diamonds are produced worldwide, according to Natural Resources Canada. Meanwhile, according to 2022 market research data of mining company Gemfields (UK), about 6 – 9 tons of emeralds were produced in 2015 from main producing countries (Colombia, Zambia, Ethiopia, Madagascar, Brazil).

According to Gemfields, tracking global production of any gemstone other than diamonds is difficult because mines are dispersed globally and are mainly operated by small companies. But these numbers cannot tell the full geological story. Both diamonds and emeralds are formed through complex processes.

“With both of these, you need a unique set of geological conditions for it all to come together correctly,” shares Evan Smith, senior research scientist at the Gemological Institute of America. .

With diamonds, these conditions start deep in the mantle, the middle layer of the Earth. According to research in the journal Gems & Gemology In 2018, diamonds formed at a depth of 150 – 200 km underground, the deepest gemstone formation on the planet.

Diamonds form as single crystals of carbon. Geologists think this happens when a change in pressure, temperature, or some chemical reaction cools molten mantle rock containing carbon, Smith said.

For diamonds to reach the depths that humans can mine, a rare volcanic eruption is needed, called kimberlite, formed from magma at a depth of about 170 – 300 km underground. On its way to the surface, kimberlite can pass through an area containing diamonds and sweep them up.

Diamonds are distributed fairly evenly in kimberlite structures, so they can be easily mined on a large scale, Smith explains. But the same cannot be done with emeralds.

Emeralds form in more complex geological structures, suitable for small-scale, hand-mining. Emerald is the green version of the mineral beryl, which gets its color from the addition of chromium and/or vanadium. Beryllium, the main element in beryl, is concentrated in igneous rocks of the continental crust. Chromium and vanadium are more common in the upper continental crust. For emeralds to form, these distinct geological environments must meet.

“You need these two elements to react to create emeralds,” shares Chris Tacker, a geologist at the North Carolina Museum of Natural Sciences. This typically occurs when rocks containing beryllium or beryl come into contact with sedimentary rocks such as limestone or shale, or when magma flows through the surrounding rocks and absorbs the chromium. For this reason, emeralds are often found in “impact zones” such as mountains, where tectonic plates collide and different geological environments meet.

The geological conditions that produce diamonds and emeralds are both exceptional, but in terms of human accessibility, emeralds are certainly rarer still.