Published on Applied Clay Science, 18 (2001) 145–155 Copyright © 2001 Elsevier Science B.V. All rights reserved. doi: 10.1016/S0169-1317(00)00042-9 Chemical, mineralogical and ceramic properties of kaolinitic materials from the Tresnuraghes mining district (Western Sardinia, Italy) M. Dondi a , G. Guarini a , P. Ligas b , M. Palomba c , M. Raimondo a , I. Uras b a IRTEC, Istituto di Ricerche Tecnologiche per la Ceramica - CNR, Via Granarolo 64, 48018 Faenza, Italy b DIGITA, Dip. Geoingegneria e Tecnologie Ambientali, Univ. Cagliari, Piazza d’Armi, 09123 Cagliari, Italy. c CSGM, Centro Studi Geominerari e Mineralurgici - C.N.R., Piazza d’Armi, 09123 Cagliari, Italy Abstract Kaolinitic materials crop out in the Tresnuraghes mining district (Western Sardinia, Italy). Three main kaolinitic deposits, located in the Patalza, Salamura and Su Fongarazzu areas, respectively, were investigated in order to assess their potential in the ceramic industry. The parent rock-types of this raw material are the Oligocene-Miocene rhyolitic-rhyodacitic ignimbrites. Chemical and mineralogical analyses were performed on representative samples of each deposit, by XRD and XRF methodologies. The chemical analyses generally show high silica and low alumina contents in all samples, typical of weakly kaolinized materials. The main mineralogical association consists of kaolinite and cristobalite with quartz and smectite as the minor components. Alunite may be present as a main mineral in the Salamura and Su Fongarazzu deposits, making these clay materials unsuitable for ceramic applications. The Patalza deposit exhibits low iron and sulphur contents, but low plasticity and excessive refractoriness. The Patalza materials can be used as unconventional raw materials to replace both kaolin and silica in white-firing bodies. Results show that the introduction of the Patalza “kaolins” was well tolerated in bodies for tableware, wall and floor tiles, without significant changes in porosity, bulk density, pore size distribution and coefficient of thermal expansion. The main drawback of using the Patalza material is the slight increase of firing shrinkage, while the main advantage is a systematic increase in mechanical resistance. Key words : applied mineralogy, ceramics, kaolinitic materials, Miocene, Oligocene 1. Introduction The main Sardinia kaolinitic mining districts (Fig. 1) are located in the Northern and Western (Romana and Tresnuraghes) and Southern zones of the island (Serrenti-Furtei). At present, only the Romana kaolin district (Ligas et al., 1997), was characterized both for the composition and the technological behaviour of its material. The Serrenti-Furtei district has been not studied because of the presence of pyrite, widespread in all deposits cropping out in the area (Asunis et al., 1983; Marini et al., 1992) and making these materials unsuitable for an use in the ceramic industry. The investigations of the Tresnuraghes mining district conclude the studies on the composition and ceramic properties of the kaolinitic materials of Sardinia. The Tresnuraghes area includes three main kaolinitic deposits (Salamura, Su Fongarazzu and Patalza) which have been mined in the past by open pits. These deposits have been investigated by several authors (Carboni et al., 1984; Garbarino and Palomba, 1990;