A rare crystalline mineral mined by forced labour on the prison asteroid Tars Lamora in Star Trek: Prodigy, beneath which the starship Protostar lay hidden.
Chimerium is a valuable crystal found deep inside Tars Lamora, the mining colony in the Delta Quadrant where Star Trek: Prodigy begins. The Diviner forces his captives, the Unwanted, to dig for it, though his real aim is to find the Federation ship buried in the rock.
In the opening story Lost and Found, Dal R'El and Rok-Tahk discover the USS Protostar hidden in a cavern beneath the mine, and the young crew escape in it with a supply of chimerium still aboard.
The mineral is needed to make certain cloaking devices work. In the episode First Con-tact the Ferengi trader DaiMon Nandi offers Dal a cloak in return for help in obtaining another people's crystals, then steals the Protostar's chimerium so that her own ship can hide.