Celestine

Celestine (strontium sulfate, SrSO4).

A crystalline mineral and useful source of strontium. Celestine dissolves quickly in seawater, but certain microorganisms synthesize it as a shell or ballast.

Local deposits must be the skeletons left by dead colonies of these organisms. The colonies may have overgrown on an artificial strontium source, then died off when the source was removed.

Strontium (Sr), element 38, is a soft and highly reactive metal with applications in radiothermal power generation. Strontium on this planet contains elevated levels of Strontium-90, a highly radioactive, bone-seeking isotope which poses a long-term health risk to human colonists. Strontium-90 is only produced in nuclear fission reactions.

Assessment: do not ingest.