Red soil known as terra rossa is the most extensive soil type in Istria. It is recognised as polygenetic paleosol but also constitutes pedo-sedimentary colluvial complexes. The intent of the present study is to determine the origin and composition of terra rossa in Istria by mineralogical, geochemical, and micromorphological methods. The coexistence of hematite and goethite, and typical average values of Fe_d (dithionite soluble iron) in terra rossa from Istria support specific pedoenvironment of terra rossa formation (Boero and Schwertmann, 1989). Kaolinite which does not form intercalation compounds with DMSO (highly disordered kaolinite), hematite and goethite represent authigenic mineral phases in terra rossa. The differences in SREE observed in terra rossa can primarily be attributed to the different REE content in parent rocks and less to fractionation during the weathering processes. External material contributions have strongly diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in Istria. This polygenetic material is mainly composed of strongly weathered and reworked loess of the Lower and, more probably, Middle Pleistocene age. It also contains (1) reworked relicts of old terra rossa-type soils which might have formed from limestones, dolomites and flysch, and (2) remains of eroded bauxites of Jurassic and Paleogene age. Due to processes of erosion and redeposition they are more or less incorporated in terra rossa. The external material observed in the upper part of some terra rossa profiles represents Upper Pleistocene loess.

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