Take a diamond with impurities to a jeweler, and you will probably be told it is worth little or nothing.

But some impure diamonds that pushed up to the surface from the Earth’s interior in China, the Republic of South Africa, and Botswana are priceless to a group of scientists, who studied them.

The researchers discovered that the impurities found in these diamonds were actually traces of Ice VII, a rare form of water that developed deep within the Earth’s crust.

To the scientists, these impure diamonds are providing the first direct evidence that pockets of liquid water may exist as far as 800 kilometers into the layer of Earth called the mantle.

It’s thought that the diamonds were formed in the mantle with temperatures that reached more than 540 degrees Celsius.

The researcher’s findings are published in a recent edition of the journal Science.