Harmotome from a new occurrence of red beds in the Upper Silesian Coal Basin (Poland)

Harmotome has been identified, using optical microscopy, XRD, IR, SEM/EDS and DTA, in an altered collapse breccia in a new occurrence of the so-called red beds in the Upper Silesian Coal Basin (“Marcel” mine). The mineral occurs in some metasomatized clasts, in the breccia matrix and in some microdruses and seald vugs. Prismatic, subhedral crystals of harmotome present in the druses are most often transparent and colourless and reach a length of 0.5 mm. In most cases, they form penetration twins with pseudo-tetragonal (morvenite type) and pseudo-orthorhombic (Marburg type) symmetry. The chemical formulae of two crystals analysed using EDS are as follows:A—Ba1.43Na0.86K0.24[Al4.38Si11.72O32] · 12 H2OB—Ba1.45Na0.84K0.20[Al4.31Si11.78O32] · 12 H2OThe harmotome originated at a last stage in the evolution of the red beds; their younger component, dioctahedral smectite, occurs only locally. The harmatome could have formed as a result of either supergene weathering of Carboniferous rocks (previously thermally altered by coal fires) or during later diagenesis of the products of these alterations when the Carboniferous strata were buried under Miocene sediments. Barium was contained in sulphate-free or sulphate-poor pore waters in the Carboniferous rocks of the coal basin.