In this study, a general defect characterization in diamond-cutting tools used in marble, granite and natural stone cutting has been investigated. An important factor determining the performance of the PCD tool and the quality of the cutting operation is the bond characteristic obtained during hot pressing as a function of the pressure, sintering temperature and time. Successful diamond tool design starts with the appropriate choice of high-quality matrix powders and diamonds. The matrix should support the diamond particles without damaging them. During cutting the matrix is expected to wear to some extent provided the tips of the diamond particles run easily and also chip flow smoothly. The bond reaction of the diamond surface and surrounding metal matrix is effective for efficient tool performance. With this type of cutting/abrasive material produced by the PM techniques the primary important factor for their properties is cleanness (cleanness of operation media, cleanness of powders and diamonds used). In general, a weak diamond-matrix bond as well as oxide films and inclusions in the matrix overtake the role of crack initiation. Also the diamond particles can act as defects through their size, form and area distribution (clustering). In this study for a microstructural optimization, the defect characterization should be realized primarily. Transverse rupture tests which are generally used for hard material were carried out with different matrix and diamond compositions. The toughness of the tested materials were determined and the defects leading to crack formation are classified. (C) 2001 Elsevier Science Ltd. All rights reserved.