Jakub Dikej: Minerals of tourmaline supergroup in hydrothermal processes Comenius University in Bratislava, Faculty of Natural Sciences, Dpt. Of Mineralogy and Petrology Bachelor thesis, 58 pages, 2014 Minerals from tourmaline supergroup are cyclic aluminio-boron-silicates with structural formula: XY3Z6(T6O18)(BO3)3V3W. The nomenclature of the supergroup is based on occupation of X-site, which divide the supergroup into alkali (X = Na1+, K1+), calcic (X = Ca2+) and X-vacant (X = □) groups. Another division into series is based on occupation W-possition, which divides supergroup into oxy-tourmaline (W = O2-), hydroxy-tourmaline (W = OH1-) and fluor-tourmaline (W = F1-) series. Tourmalines crystallize in trigonal system, with point group 3m and space group R3m. They usually form prismatic crystals with hexagonal or ditrigonal section. They also can form acicular to fibrous agregates accumulating parralelly or radialy. Tourmalines belong among the most variable minerals in colour. Their hardness in Mohs scale is 7 to 7,5 and density varies from 2,9 to 3,3 g.cm-3. Substitutions occuring in structure of tourmaline can be homovalent or heterovalent, they can exchange 2 cations or anions, but also there can be present complex substitution, when 3 or more cations or anions are exchanging. In hydrothermal processes tourmalines are present in different enviroments, which can be divided to: 1) granitoid-related deposits; 2) veins in volcanic rocks; 3) veins in metamorphic rocks; 4) various types of stratabound ores, in both metasedimentary and metavolcanic terranes (Slack, 1966). In Slovakia there is an abundance of localities with tourmaline minerals. Čučma - Gabriela was selected as model locality, from which sample was analysed by electron microprobe and powder X-ray diffractometry. Microprobe analyses revealed, that two dominant substitutions control the composition: uvitic/feruvitic Ca(MgFe2+)(NaAlFe3+)-1 and magnezio-foititic X□AlFe3+(NaMgFe2+)-1. Main mass of tourmalines from analysed specimen belong to feruvite, smaller areas belong to schorl-dravite and the rim of crystals in some places is magnesio-foitite. Key words: tourmaline, boron, crystallography, crystal chemistry, hydrothermal process, vein mineralizations, stratiform mineralizations, Gemeric superunit