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

A somewhat different mineral assemblage is known from the Jurassic sedimentary rocks (especially the limestones) where manganese minerals (manganite, romanechite) and hematite, goethite are found. Massive limestones which have been quarried for centuries (and are still quarried today) around Tardosbánya owe their reddish brown colour to hematite and goethite, and are used as ornamental stones. In Medieval times this rock was used for palatial buildings at Esztergom, Visegrád, Royal Buda, and elsewhere. At the Eocene and Cretaceous bauxite deposits around Nagyegyháza and Gánt, the chief aluminium minerals are böhmite and gibbsite. Large aluminite concretions are also common at Nagyegyháza. Calcite and siderite occupy fractures in the sediments where goethite and hematite pseudomorphs, derived from the decomposition of iron sulfides, are also found. Investigations have shown that the deposits also contain microscopic quantities of many other minerals. Extremely well developed crystal groups of gypsum found in the overlying clay near Gánt were famous. Bauxite from near Gánt and Iszka-szentgyörgy was extracted by open-cast mining on a huge scale from the 1920's (from the 1940's onwards about 10 million tons of bauxite were removed from the deposit near Gánt) before all the mines were shut down. Eocene coal deposits which were discovered by systematic prospecting at several places (Dorog, Tokod, Sárisáp, Tatabánya, Bajna, Bicske, Mány, Oroszlány) have a rich mineral assemblage (Fig. 52). Primary minerals found here are often similar to those found in other mountains (pyrite, marcasite, calcite, quartz) but in the deposit at Csordakút, near Bicske a number of interesting organic minerals (mellite, humboldtite, whewellite) were also detected (Fig. 53). Because of their large size, the mellite crytals (up to 10 cm) and crystal groups (up to 50 cm) found here became famous all over the world (Fig. 54). Of the secondary minerals, gypsum is quite common (splendid specimens were obtained from overlying clays, particularly from Bajna; Fig. 55). Less common are tschermigite, jarosite, epsomite, rozenite, aluminite, and alunite. At one time, concretions consisting predominantly of aluminium hydroxides (böhmite, gibbsite) were