Dunántúli vörösagyagok fizikai és kémiai tulajdonságai | Physical and chemical properties of red clays in Transdanubia

The properties of red clays in Transdanubia were characterized on the basis of analysed representative profiles, which were chosen from a large number of samples for the evaluation. Data on the mechanical composition, the values of the exchangeable cations and adsorption capacity, and the mineral composition determined by X-ray diffraction and thermo-analytical analysis were used to characterize the red clays. On the basis of conclusions drawn from the analytical results, the red clays in Transdanubia can be divided into the following groups. 1. Red soils on the western periphery of Hungary a) Red soils in the Kőszeg Hills . The hard red clay layers can be found either above or between various shale layers. Most of the red clays are old in situ formations. There is a small quantity of quartz, and feldspar, kaolinite, illite and a small amount of gibbsite, hematite and goethite can also be found in the fine fraction. b) Red soils in the Őrség region . These soils occur in several places in various silt, sand and gravel layers, alternately or combined. These soils were transported from their site of origin by rivers and surface waters. In some cases they are mixed with loess. Total chemical analysis and mineral composition revealed the presence of disintegrated siallite and very old ferralite. The soils have a relatively high kaolinite content. 2. Red soils formed on Permian sandstone . Permian sandstone is probably the oldest soil type in the country. Permian sandstone was formed from tropical red earth sediment. These red soils have a bright red colour, sometimes with a hint of purple. Naturally the present soil formed from the Permian stone is not a Paleozoic relic, but is a soil residuum from the end of the Tertiary period. It can be found in some parts of the Balaton Uplands, for example at Balatonalmádi, Balatonszepezd and Kővágóőrs. This soil characteristically contains kaolinite, illite, montmorillonite and hematite. Similar soil types can be found in the Permian sandstone area of the Mecsek Hills (e.g. Kővágószőlős). These contain no kaolinite or hematite, but do contain goethite. 3. Bauxitic formations in the High Transdanubian Hills . Hungarian bauxite was formed on the surface of Mesozoic limestone and dolomite tables. Red clays can be found in the upper layers of eroded bauxite. These clays are residues of Tertiary tropical and subtropical soils and can be divided into two groups. a) Red clays in which the allite combination is dominant . On the basis of total chemical analysis, the molecular ratio of these soils is similar to the oldest tropical soils. The type of weathering was ferrallitic. These soils contain a high amount of boehmite and gibbsite, but little ferric oxide. They contain a small percentage of quartz, 30–40% kaolinite, but no illite or montmorillonite. b) Bauxitic red clays exhibiting allitic characteristics . Allitic characteristics can be seen in their mineral composition and there are early signs of ferrallitic decomposition. These soils contain a high quantity of quartz and a substantial amount of kaolinite and chlorite. They also contain illite, montmorillonite and mica, and small quantities of boehmite, gibbsite and hematite. 4. Red clays in the Low Transdanubian Hills . a) Red clays produced by the weathering of the Pannonian surface . These have a medium clay content and the clay minerals include substantial quantites of illite, chlorite, montmorillonite and kaolinite. Gibbsite and hematite could also be detected, but their red colour is generally attributable to amorphous iron compounds. These soils were formed in the period between the end of the Miocene and the beginning of the Pleistocene. b) Red clays in the Mecsek and Villányi Hills . These can be found on the surface and in the fissures of limestone. The clay minerals include kaolinite, montmorillonite and illite with small quantities of gibbsite and amorphous iron. They are terra-rossa formations, created by Mediterranean weather conditions.