Brewsterite-Ba and Harmotome from the Wicklow Lead Mines, Co. Wicklow, Ireland

Abstract:The zeolite group minerals brewsterite-Ba and harmotome occur as minor latestage primary phases in the low-temperature Pb-Zn veins at Glendalough and Glendasan, Co. Wicklow. Brewsterite-Ba was identified on a single specimen from the Old Luganure Mine. Harmotome occurs at the Glendalough Mine, the Foxrock Mine and the Old Luganure Mine. Quantitative analyses of crystals of brewsterite-Ba reveal the most barium-rich composition yet reported: ($Ba_{1.88},Sr_{0.02},K_{0.01},Na_{0.01}$) [$Al_{4.03}Si_{12.02}O_{32}$]-$nH_{2}O$. This is close to the hypothetical barium end member. The harmotome is also barium-rich. It contains lesser amounts of sodium and potassium, but no calcium. This is the first record of brewsterite-Ba from Ireland.