Ž . Geoderma 91 1999 125–150 Mineralogical and geochemical indicators of the polygenetic nature of terra rossa in Istria, Croatia G. Durn a, ) , F. Ottner b,1 , D. Slovenec a a UniÕersity of Zagreb, Faculty of Mining, Geology and Petroleum engineering, PierottijeÕa 6, HR-10000 Zagreb, Croatia b UniÕersity of Bodenkultur Vienna, Department of Applied Geology, Peter Jordan Strasse 70, A-1190 Vienna, Austria Received 11 March 1997; accepted 23 November 1998 Abstract Terra rossa in Istria is situated on the Jurassic–Cretaceous–Paleogene carbonate plain and is Ž considered a polygenetic reddish soil which bears typical terra rossa Fe-oxide characteristics e.g., . Fe and Fe rFe . The difference in particle size, mineralogy and geochemistry observed between d d t terra rossa and the insoluble residue of limestones and dolomites clearly indicates that the additions of external materials might have diminished the influence of insoluble residue of limestones and dolomites as the primary parent material of terra rossa in Istria. Terra rossa is clay Ž and silty clay composed of quartz, plagioclase, K-feldspar, micaceous clay minerals illitic . Ž . material and mica , kaolinites Kl and Kl , chlorite, vermiculite, low-charge-vermiculite or D Ž . high-charge smectite, mixed-layer clay minerals other than illitic material , hematite, goethite and XRD-amorphous inorganic compound. Calcite, dolomite and boehmite are sporadically present and are of local importance. Kaolinites and illitic material are dominant clay mineral phases in the clay fraction of all terra rossa from Istria. Kaolinite which does not form intercalation compounds Ž . with dimethylsulfoxide DMSO is the dominant mineral phase in fine clay and is considered predominantly authigenic rather then inherited from parent materials. Neither the content and particle size distribution nor the bulk and clay mineralogy of the insoluble residue of limestone and dolomite support development of terra rossa entirely by dissolution of carbonate rock. If terra rossa has developed only from the insoluble residue of limestone and dolomite, its clay content, due to weathering should be higher than that in the insoluble residues which is not the case. Plagioclase was found only in one insoluble residue while all terra rossa samples contain this ) Corresponding author. Tel.: q385-1-4836067; Fax: q385-1-4836057; E-mail: gdurn@rudar.rgn.hr 1 Tel.: q43-1-47654-5407; Fax: q43-1-47654-5449; E-mail: ottner@mail.boku.ac.at 0016-7061r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0016-7061 98 00130-X