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

The Miocene pebbly sandstones encircling these mountains often contain opalised and silicified wood, including the remains of large tree trunks: these are to be found in the beds of many of the streams in the area. Along the southern border of the mountains, just below the surface, huge Pliocene lignite deposits were found during the last few decades. The power station at Visonta became the chief recipient and user of this lignite which is removed by extensive open cast mining. Apart from the primary minerals (pyrite, marcasite and quartz) found here there are also some very recently formed secondary minerals (mainly sulfates). Stream-derived deposits from along the margins of these mountains have provided some interesting minerals. Placers and mineral gravels, which are still being formed at present, include a varied collection of heavy minerals. Since these alluvial deposits were largely derived from the erosion of Miocene volcanic tuffs, their mineral content provides us with valuable information about the (resistant) minerals found within them.