Csengeri Piroska - Tóth Arnold (szerk.): A Herman Ottó Múzeum évkönyve 54. (Miskolc, 2015)
Természettudomány - Fehér Béla: Turmalin kötőanyagú hidrotermás breccsa Miskolc-Bükkszentlászlóról
Turmalin kötőanyagú hidrotermás breccsa Miskolc-Bükkszentlászlóról 23 TOURMALINE-CEMENTED HYDROTHERMAL BRECCIA FROM MISKOLC-BÜKKSZENTLÁSZLÓ, BÜKK MTS., HUNGARY Keywords: tourmaline, schorl, hydrothermal breccia, Bagolyhegy Metarhyolite Formation, Miskolc-Bükkszentlászló The area around Miskolc-Bükkszentlászló is built of Triassic (Upper Ladinian-Lower Carnian), green or pale greyish green, foliated rhyolite tuff (Bagolyhegy Metarhyolite Formation), which was undergone low-grade regional metamorphism belonging to the prehnite-pumpellyite-quartz facies. According to the radiometric K/Ar age (95—104 Ma), the metamorphism took place in the Upper Cretaceous. This rock can be studied in natural outcrops, eg. along the Hideg-víz Stream. As a result of the Alpine metamorphism, fissure fillings developed along the faults within the rhyolite tuff. The fillings consist of quartz and alkali feldspars (orthoclase and albite). In some places the quartz-feldspar veins were brecciated through hydrofracturing, and the rock fragments were cemented by black, cryptocrystalline tourmaline. The lateral dimension of the brecciated zone is unknown, because this rock type has been collected solely from the debris so far, while the maximum thickness of that is about 5 cm. According to the electron-microprobe analyses the tourmaline can be classified as schorl with rather restricted chemical variability at the X and Y sites and uniform chemistry at the Z, T, V and W sites. From the average chemical composition, the structural formula of the tourmaline can be written as (Na070[]026Ca0 04)E=100 (Fe2\.78Mg0.94A10.i2Ti0.04Mn0.0i)E=2.89A16.00(Si6.06Oi8)(BO3)3[(OH)3.99F0.0i]z=4.00' The components, necessary to the formation of tourmaline, originated from the rhyolite tuff during a metamorphic event, which was confirmed by the AFM diagram. In the cement material K-feldspar can also be found beside tourmaline. Finally, the brecciated rock with tourmaline matrix was cross-cut by subsequently formed quartz-orthoclase veinlets. [Translated by the author] Fehér, Béla
