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

from a few cms to a decimeter in length in many quarries (Miskolc-Tapolca, Eger-Felnémet, Miskolc-Omassa, Bélapátfalva; Fig. 20). These quarries were opened primarily for the cement industry. In the limestone caves of the region, calcite is the most frequently encountered mineral. It is at its most abundant, and most diverse in form in the caves of Bükk, where earthy phosphate minerals derived from the guano deposits are also found. An iron ore deposit of hydrothermal origin (in a dolomite host-rock), was found in the Uppony mountains near Uppony. This has been mined for decades on a small scale. Jurassic basic, and ultrabasic igneous rocks occur in the Western part of these mountains. Exploratory mining (prospecting) around Szarvaskő revealed a sulfide association (chalcopyrite, pyrrhotite and pentlandite) as well as an oxide one (magnetite and ilmenite) typical of early crystallisation that is rare in Hungary. During the main crystallisation process some of the more common rockforming minerals (including hornblende and plagioclase) were formed as large, often several centimeter long, easily visible, crystals (Fig. 21). The hydrothermal quartz-calcite veinlets include a peculiar mineral assemblage rich in prehnite (Fig. 22). Rocks from this area are quarried for road-building purposes and to a lesser extent for the manufacture of ornamental stones. Since some of the rock types (such as wehrlite) contained a lot of iron and titanium and a little nickel and vanadium, attempts were made to use them metallurgically, but this was not successful because of the high silica content of the rocks. From sedimentary rocks of the Oligocène in the region of Eger and Demjén, several manganese carbonate deposits and showings are known, with finely granular rhodochrosite as the chief ore mineral. Near the surface, this pink mineral has become oxidised and is dark brown in colour. Although the oxidised ore has a higher manganese content, it is still not suitable for the extraction of manganese. Along the margins of the Bükk and Uppony mountains in the Miocene sedimentary strata, commercially viable coal deposits were found in many places and these were mined until recently at over 50 localities (today there are just a few working mines left). Coalmining in the Sajó valley began in the 18th century but a