It’s been 15 years since the global effort to ban conflict diamonds began ... has funded a school to get ­children like 12-year-old Kalala Ngalamume out of the mines and back into class.

Synthetic stones also profit from the blood-diamond narrative that the proceeds of gem mining, in the case of producers including Sierra Leone and Central African Republic, has financed civil wars.

As countries race to secure supplies of rare earth elements and battery metals, Japan’s deep-sea mining efforts could offer a strategic advantage, reducing reliance on imports and bolstering its ...