CelestineCelestine (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.
