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Rare blue diamonds are born deep in Earth’s mantle

Sinking ocean tectonic plates may deliver key ingredients for making blue-tinged gems

blue diamond

BLUE GEM  This boron-bearing blue diamond, about 1.26 centimeters long, contains tiny bits of minerals that suggest it formed deep in Earth’s mantle.  

Robison McMurtry/© 2018 GIA

By Carolyn Gramling

- More than 2 years ago

Blue diamonds, among the rarest gems on Earth, are born deep inside the planet’s mantle.