Origin of ultra-pure Golconda diamonds

The famous transparent and sparkling Golconda diamonds may originate from volcanic quarries 300km from where they are mined .

Researchers may have found the true origin of famous Golconda diamonds like Hope or Koh-i-noor, Live Science reported on April 21.

Hope Diamond - one of the most famous gems in the world. (Photo: Telegraph).

Golconda diamonds are special because they have very few impurities and little nitrogen, so they are extremely clear and free of sparkle-reducing blemishes. They are also very large. The Koh-i-noor diamond, currently in the collection of British Royal ceremonial items kept at the Tower of London, weighs 105.60 carats. The Hope Diamond, displayed at the Smithsonian National Museum of Natural History in Washington DC, USA, weighs 45.52 carats.

These Golconda diamonds were discovered in southern India between the 1600s and 1800s. They were mined in placer mines - shallow holes cut into riverine sediments. But before that, diamonds were brought to the Earth's surface in large blocks of volcanic rocks called kimberlites , and experts don't know where the kimberlite rocks containing these diamonds came from.

New research published in the journal Earth System Science suggests that Golconda diamonds may originate from the Wajrakarur kimberlite mine in Andhra Pradesh, India , today, about 300 km from where they were mined.

To trace the origin of Golconda diamonds, geologists Hero Kalra, Ashish Dongre and Swapnil Vyas from Savitribai Phule Pune University studied the chemistry of the surrounding kimberlite and lamproite rocks. These are rocks that form at the base of the Earth's crust and upper mantle, where most diamonds form.

The team discovered that kimberlite from the Wajrakarur mine could have been pushed up from the depths where diamonds form and contains minerals that often appear with diamonds. They then conducted surveys using remote sensing data such as satellite images, vegetation and humidity measurements. Surveys reveal that an ancient river that dried up long ago may have transported diamonds from Wajrakarur to the Krishna River and its tributaries, where the diamonds were found.

However, this result is not certain, according to Yakov Weiss, a geochemist who studies diamonds at the Hebrew University of Jerusalem. In the new study, the authors studied the geochemistry of common diamonds from the lithosphere - the Earth's hard crust and upper mantle - and determined that the Wajrakarur deposit may contain diamonds. However, Golconda diamonds form at greater depths in the mantle, perhaps in a transition zone near the Earth's core.

It is difficult to directly detect the origin of Golconda diamonds because they do not have the liquid inclusions from the mantle where they begin to form. This makes them beautiful and popular, says Weiss, but provides little information to geochemists. Therefore, Golconda diamonds will probably always retain mysteries.