Until the discovery of diamond mines in Brazil in 1725, with the sole exception of a few black diamond crystals found in the mountains of Borneo, all the world’s diamonds came from India. Ancient Indian diamonds were alluvial: they were not mined so much as sieved and extracted as natural crystals from the soft sands and gravels of ancient riverbeds. Originally ejected from the host rocks – kimberlite and lamproite – by primeval volcanoes, they were swept up by water and transported along rivers, until at last they came to rest when the river died, many millions of years ago. Most such
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