Formation of marine barite (BaSO4) concurrent with dissolution of acantharian celestite (Sr/Ba, SO4) was examined under laboratory conditions in this work. Acantharian cysts, composed of barium-enriched celestite (Ba/Sr mole fraction ∼0.003), were allowed to react for 21–158 days in small volumes of natural seawater (20 to 100 μl) sealed within Teflon tubes. In 17 trials, three experiments yielded single barite particles, and one experiment produced barite overgrowth on a siliceous particle. These observations are consistent with a barite formation pathway in which acantharian dissolution within microenvironments leads to BaSO4 supersaturation and subsequent barite formation. This work supports the significance of Acantharia as one potential source of strontium-rich barite particles that are ubiquitous in the oceanic water column.