By the numbers: Ukraine has about 5% of the world's total reserves of critical rare earths, per UN data. Zoom out: Ukraine, according to its national Geological Survey, has largely untapped reserves of minerals like tantalum, beryllium and niobium.

China plans to prohibit non-state companies from mining rare earths, further tightening its control over a strategic sector that has emerged as a battleground in its trade war with the US.