The distribution of barytocalcite and alstonite in the Northern Pennine Orefield

SUMMARY The rare minerals barytocalcite and alstonite, the dimorphs of barium calcium carbonate, are shown to be of widespread occurrence in the barium-bearing deposits of the outer zone of the Northern Pennine Orefield where they generally accompany witherite. Barytocalcite in particular is present in much greater abundance than hitherto supposed and in several deposits is shown to be the dominant barium mineral. Both minerals are abundant only in deposits within a limestone wall rock and are considered to be the products of reaction between late-stage mineralising fluids and the wall rock.