Nowadays, in order to produce the high strength concrete in the civil engineering applications, the use of different types of admixtures is well-known. In general, these materials are either chemical or mineral products. In this paper, the formations of amorphous silica of Isparta Region are defined in a technical manner and their use in the concrete manufacturing as a natural pozzolan is evaluated. The effectiveness of amorphous silica in making high strength concrete material is analysed experimentally, and the research findings are discussed. (c) 2005 Elsevier Ltd. All rights reserved.