Light-blue barite from Jebel Ouichane in Morocco forms blade-like tabular crystals (up to ca. 10 cm) with superb transparency and lustre. It represents one of the most spectacular gem-quality specimens in the world. The barite is hosted by iron-ore-bearing skarns, developed within Jurassic-Cretaceous limestones, and occurs in close spatial association with calcite. Although it exhibits simple chemical composition, some irregular sectorial zoning, maintained by elevated contents of Sr in various crystal domains, were found. Barite from Ouichane is abundant in one phase (liquid or gas) or two-phase (liquid-gas) fluid inclusions of primary, pseudosecondary, and secondary origin. A combination of fluid inclusion microthermometry and stable isotope data suggest that δ18O value of barite-forming solutions, resulting from mixing of meteoric waters with hydrothermal fluids, could be in the range from -3,5‰ to +2,7 ‰ (VSMOW), whereas the main barite crystallization stage falls in the temperatures range of 160-180 °C. The recorded first ice melting temperatures (-35.9 to -41.5 ºC) indicate the presence of divalent cations, i.e. Ca2+and Mg2+ in addition to NaCl ± KCl in the mineralizing fluid composition. The possible source of SO42- and Ba2+, which gave rise to the barite formation was fluid enriched in Ba, Sr, Ca, Mg, S, and other elements derived from the alteration of carbonate and silicate minerals, being components of sedimentary and igneous rocks found in the surroundings of Nador area. Necessary amounts of sulphur could be in turn provided by weathering of pyrite and/or decomposition of organosulphur compounds. The combination of δ34S and δ18O values of barite (+16.39‰ and 6.71‰, respectively) indicate that its formation occurred in a steam-heated (near-surface) environment.