Umbrisols, a reference soil group of the World Reference Base for Soil Resources, are defined by the umbric horizon, which is characterized by structure, accumulation of soil organic matter (SOM), dark colour, low “base” saturation, and thickness. Our exemplary study focussed on typical horizons of four Umbrisol profiles developed from paragneiss or granite in the Black Forest (South Germany). To deepen our understanding of Umbrisol formation and properties, we characterized pedogenic species that are involved in SOM stabilization, including short-range ordered aluminosilicates (SROAS), hydroxy-interlayered minerals (HIMs), extractable aluminium (Al) and iron (Fe) species, and SOM itself. All mineral horizons under study had sandy texture (>51% sand) and acidic pH (3.2–4.7). The large proportion of dithionite-extractable Fe relative to total Fe (up to 55%) indicated intensive weathering. Large fractions of Al and Fe were in organic association, as derived from further extraction with oxalate, citrate-ascorbate, and citrate. Soil organic carbon contents of up to 103 g kg−1 reflected SOM accumulation with C:N ratios ranging from 14 to 29. SOM was generally thermally stable, and 13C nuclear magnetic resonance spectroscopy revealed the contribution of black carbon to SOM, possibly as a remnant of historical charcoal production, typical of forested German low-mountain ranges. Far-infrared spectroscopy indicated imogolite-type SROAS, increasing with soil depth. X-ray diffractometry revealed the dominance of quartz, feldspars, micas, and interstratified phases in all horizons. HIMs formed progressively with depth. Both HIMs and SROAS have formed; their formations do not exclude each other. Irrigation experiments pointed to partial equilibrium dissolution of imogolite-type SROAS and their colloidal transport. Al and Fe were mostly released in colloidal form. Dissolved OM eluted reflected the presence of black carbon in soil. Together with HIMs, Al-SOM associations and SROAS formed as in Andosols, but to lesser extent. HIMs and SROAS may affect SOM stabilization in the subsoil more strongly than in the topsoil, where Al-SOM associations may largely contribute to stabilization. However, mechanistic studies on SOM stabilization and mineral formation in Umbrisols are scarce yet and require further attention particularly regarding Umbrisols formed in different climates.