WASHINGTON, (Reuters) – A dirty-looking, commercially worthless brown diamond found in Brazil is yielding priceless information about the composition of a layer deep inside our planet.

The diamond contained a mineral called ringwoodite that entrapped a significant amount of water, an international team of scientists reported this week.

The discovery of the water-rich mineral indicates that mammoth amounts of water are trapped in a zone 410 to 660 kilometers (255 to 410 miles) beneath the surface between Earth’s upper and lower mantle, the researchers said.