Greece is a major bentonite producer, with Milos Island being one of the largest bentonite mining centres in the world. In addition to the bentonite deposits which are well known, various other occurrences exist in the islands of Chios and Samos, Eastern Aegean and in some areas of Thrace, in NE Greece. These bentonites are associated with volcanic activity and their age ranges from Lower Oligocene in Thrace, to Lower–Middle Miocene in Chios and to Upper Miocene in Samos. Although some of these materials have been utilized since ancient times (e.g. the Samian Earth), these bentonites have been mined only at a local scale. In this study the first data on the mineralogical and geochemical characteristics of these bentonites are presented.
The Samos bentonites of UpperMiocene age are medium–lowgrade (40–70% smectite) and crop out in the SE margin of the Karlovasi Basin formed at the expense of acidic pyroclastic flows mainly in a subaeriallacustrine environment. They consist mainly of Ca-rich medium–high-charge montmorillonite, opal-CT and sanidine with minor quartz and locallymordenite. The Chios bentonites of Lower–MiddleMiocene agewere formed at the expense of trachyandesitic tuffs in a lacustrine environment in the Neogene Basin at theSEpart of the island. They consist mainly of Ca,Mg-rich high-charge montmorillonite (33–75%), similar to the SAz-1, and opal-CT, minor plagioclase, chlorite, plagioclase, carbonates and traces of talc and serpentine. In Thrace, LowerOligocene pyroclastic flows, tuffs and lavas of acidic-intermediate compositionwere altered to zeolites and bentonites in the sedimentary basins of the Feres-Pefka, Skaloma and Sappes areas. The parent pyroclastic rockswere altered to Ca-rich and in places,Na-rich, dioctahedralmontmorillonite or Fe-rich beidellite (Sappes area) and with minor opal-CT,mordenite, quartz, plagioclase and, in places, illite. The bentonites are medium–high grade (50–58% smectite in Feres-Pefka, 74–86% in Skaloma and 29–40% in Sappes).
The bentonites havemoderate cation exchange capacity andmoderate/lowswelling index and viscosity and they are not suitable for the drilling and foundry industries. However, preliminary results show that after processing, most of the depositsmight be utilized in high added-value applications such as bleaching earths or in the synthesis of clay-based polymer nanocomposites.