Promethium

Promethium is one of the rarest elements on Earth — only about 500 grams exist naturally in the entire planet's crust at any given time! Named after Prometheus, the Greek Titan who stole fire from the gods and gave it to humanity, it was first produced artificially in 1945 by Jacob Marinsky, Lawrence Glendenin, and Charles Coryell at Oak Ridge National Laboratory.

All of promethium's isotopes are radioactive, which is why it is so rare in nature — it simply decays away. Promethium has been used in luminous paint for watch dials and nuclear-powered batteries for spacecraft and guided missiles. Promethium-147 is used in thickness-measuring instruments in factories. Its glow is a faint blue-green that fades as the isotope decays.

Promethium's symbol 'Pm' is a distinctive two-letter element in Spellement. While 'pm' is not common at word beginnings, partial emphasis allows spellers to use 'p' or 'm' individually — both frequent English consonants that open up many creative word-building possibilities.