Tag: Copper refining

With an average concentration of only about 90 parts per billion in the Earth's crust, selenium is indeed one of the rarer elements, found in three to seven orders of magnitude less abundance than major rock-forming elements. While it is a naturally occurring element, its rarity in significant concentrations means it is almost never mined directly.

Despite being present in the Earth's crust at a low concentration of just 0.05 to 0.09 parts per million, the question of "is selenium rare or common?" has a surprisingly nuanced answer. It is simultaneously geologically rare but commercially accessible due to its method of extraction.