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

hydroquartzite (as found primarily in the region of Gyöngyössolymos, Gyöngyösoroszi, and Gyöngyöstarján). Here, chalcedony, the main mineral, appears in a variety of colours due to the presence of hematite, goethite, manganese oxides, and celadonite. The most beautifully coloured and most 'eye catching' specimens are cut and polished and made into gemstones or used as ornamental stones (Fig. 38). Rhyolites of the Mátra rhyolite occupy only a very small area and are typified by a restricted assemblage of hydrothermal minerals including opal, goethite, nontronite, and jarosite. Finally, the minerals associated with the deposits of coal and lignite encircling the Mátra should be mentioned. As elsewhere, in similar deposits, these may be primary, e.g., quartz, pyrite and marcasite, or secondary (gypsum, sulfur, thenardite, and portlandite). The Nógrád coal deposits, which are found in part of the Cserhát mountains, where first mined in the 19th century at the time of the War of Independence of 1848 but these deep mines have long been abandoned. At the foot of the Mátra near Visonta, however, large scale open cast mining is still going on today, primarily supplying the Visonta power station with raw material.