The karst bauxites from the Apulian carbonate platformsouthern Italy.have an ooidic texture. The concretions, which are formed at the expense of the kaolinitic matrix, are composed of Al-hematite in the core and of Al-hematite and boehmite in the banded cortex. The Al-hematite in the core has an average formulaAl0.12Fe0.88.2O3 and the Al is within the range of values observed in hematite formed through in situ epigenetic replacement of kaolinite. The Al substitution in hematite involves a water-unsaturated environment, possibly promoted by fluctuations of the groundwater table followed by intense drainage and evaporation. In the banded cortex, boehmite may form instead of Al-hematite at lower water activity values. Further, the boehmite stability increases for high values of the a 3qra3 Al Hq ratio, which is mostly controlled by the pH of the solution. The stability of the Al-hydroxide decreases with increasing pH.

Ferrouginous concretions in a Late Cretaceous karst bauxite: composition and conditions of formation

ACQUAFREDDA, Pasquale
1999

Abstract

The karst bauxites from the Apulian carbonate platformsouthern Italy.have an ooidic texture. The concretions, which are formed at the expense of the kaolinitic matrix, are composed of Al-hematite in the core and of Al-hematite and boehmite in the banded cortex. The Al-hematite in the core has an average formulaAl0.12Fe0.88.2O3 and the Al is within the range of values observed in hematite formed through in situ epigenetic replacement of kaolinite. The Al substitution in hematite involves a water-unsaturated environment, possibly promoted by fluctuations of the groundwater table followed by intense drainage and evaporation. In the banded cortex, boehmite may form instead of Al-hematite at lower water activity values. Further, the boehmite stability increases for high values of the a 3qra3 Al Hq ratio, which is mostly controlled by the pH of the solution. The stability of the Al-hydroxide decreases with increasing pH.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11586/44765
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 37
  • ???jsp.display-item.citation.isi??? ND
social impact