The Middle Jurassic Opalinus Clay (OPA) in Switzerland and southern Germany is regarded as a potential host rock for the disposal of high-level radioactive waste. This study investigates sediment samples from drill cores taken from the Swabian Alb region (southern Germany), and employs a facies-based approach combined with mineralogical analyses, measurements of cation exchange capacity (CEC), LECO and Rock-Eval pyrolysis. Results are based on analyses of two fully cored scientific drillings conducted by the Federal Institute for Geosciences and Natural Resources (BGR) in the framework of the research project "SEPIA" in the Swabian Alb in Baden-Württemberg, southern Germany. The drill sites are located in the vicinity of the villages Metzingen (48.51149° N, 9.26464° E) and Röttingen (48.89905° N, 10.29520° E). At the drilling sites, the OPA is between approx. 100 m – 150 m thick and overlain by 50 m – 70 m of overburden. In Germany, the OPA can be lithostratigraphically divided into two subunits: the Teufelsloch member and the overlying Zillhausen member. This division is based on a combined lithological and stratigraphic framework (Dietze et al., 2021). Regarding lithofacies, the OPA in Switzerland and southern Germany can be broadly divided into several distinct units ("facies associations" according to Zimmerli et al., 2024). For Germany, the following three lithological facies associations (FA) were identified based on a subfacies approach: (1) a lower part that is rich in clay (FA-1), (2) a middle part that is silty (FA-2) and (3) an upper part that is silty and interbedded with calcareous(-sandy) beds (FA-3).XRD patterns of whole rock material were recorded using a PANalytical X'Pert PRO MPD θ - θ diffractometer (Co-Kα radiation generated at 40 kV and 40 mA). The samples were investigated from 3° to 80° 2 θ with a step size of 0.03° 2 θ and a measuring time of 3 sec per step. Quantitative Rietveld refinements of the experimental XRD data were conducted using the software Profex/BGMN (Döbelin & Kleeberg, 2015; Bergmann et al., 1998). Determination of cation exchange capacity (CEC) was carried out using always two different samples masses (typically 400 and 600 mg) according to the method of Meier and Kahr (1999), based on a Cu(II)triethylentetramine complex ("Cu-trien method") and measurement using VIS spectroscopy. According to Dohrmann et al. (2012), the analytical error as determined for high-CEC bentonites is generally smaller than ±3.9 cmol(+)kg-1. The total carbon (TC), total organic carbon (TOC), and total sulfur (TS) were determined using a LECO CS-230 system (Laboratory Equipment Corporation). Samples were heated up to 2000 °C under an oxygen atmosphere and an infrared detector subsequently measured the amount of produced CO2 and SO2. TOC was measured the same way after removing inorganic carbonates using 10 % HCl solution at 80 °C. Rock-Eval Pyrolyses were performed on a Rock-Eval-6 analyser (Vinci Technologies) using up to 180 mg initial sample material and a standard program (Espitalié et al., 1977; Lafargue et al., 1998), starting isothermal with 300°C for 3 min, succeeded by a heating rate of 25°C/min up to 650°C. Standard deviations for hydrogen indices (HI) and Tmax values are ± 5 % and ± 2°C, respectively.The findings of this study underscore the importance of integrating lithofacies studies with mineralogical investigations to effectively assess the variability and comparability of clay-rich host rocks suitable for radioactive waste disposal.