Alstonite, also known as bromlite, is a low temperature hydrothermal mineral that is a rare double carbonate of calcium and barium with the formula BaCa(CO₃)₂, sometimes with some strontium. Barytocalcite and paralstonite have the same formula but different structures, so these three minerals are said to be trimorphous. Alstonite is triclinic but barytocalcite is monoclinic and paralstonite is trigonal. The species was named bromlite by T. Thomson in 1837, and alstonite by August Breithaupt of the Freiberg Mining Academy in 1841. Both of these names, derived from the locality, have been in common use.