Szakáll Sándor - Jánosi Melinda: Minerals of Hungary (Topographia Mineralogica Hungariae 4. Miskolc, 1996)

localities several morphologically distinctive types of deposits occur: stratified, lenticular, brecciated, cavity infill, nested and sack-like. The mineral assemblages of these bauxite deposits are varied, because they were formed by different processes. Since these deposits were not formed in situ they contain minerals which were transported to their present position (corundum, anatase, tourmaline). During syngenetic mineral formation (after transportation, and after the bauxite had settled), the most important aluminium minerals (böhmite, gibbsite) and the main accessories (goethite, hematite) formed. Ooids, pizoids and pisolites found in bauxite were formed during the main process of so-called diagenetic mineral formation. Pyrite and marcasite, both common in bauxite, appeared towards the end of this process. So-called epigenetic mineral formation took place in deposits already covered by a superincumbent layer. During this stage, some aluminium minerals were transformed and carbonates (calcite, siderite) and iron oxides (goethite, hematite) were deposited in the cracks (Fig. 64). Finally, after the overlying strata or layers were destroyed, during the so-called hypergenetic phase, near the surface, iron oxides and iron sulfates appeared as decomposition or weathering products of iron sulfides. Nests or crusts of gibbsite, alunite and aluminite were formed from aluminium minerals already there. At the same time, and also as the products of oxidation processes, the manganese oxides, lithiophorite and todorokite were quite common. Tertiary and Quaternary sedimentary rocks have very monotonous mineral assemblages. In argillaceous rocks, pyrite, marcasite and gypsum are abundant. In the coal deposits of Várpalota, Dudar, Balinka, and Herend, the usual assemblage of primary minerals calcite, quartz, pyrite, and marcasite - is accompanied by jarosite and gypsum. In sandstones and argillaceous rocks of the Keszthely mountains marcasite and pyrite concretions, deposited from thermal springs, are found at many localities. A sulfide-sulfate assemblage must be mentioned here. It was discovered in a Quaternary pebbly conglomerate near Lesenceistvánd, where the pebbles are sometimes cemented together by marcasite. As a result of the decomposition of mar-