The brittle intercrystalline fracture (BIF) in iridium and low plasticity of this refractory fcc-metal in polycrystalline state for wide temperature range, give occasion to supposition that a metal having fcc lattice can be brittle substance like silicon due to specific features of interatomic bonds. On the other hand, experience has shown that such behavior of fcc-metal should be impurity induced effect. High plasticity of iridium single crystals ( by means of octahedral slip), which however cleave under tension, does not support idea on "classic" inherent brittleness of this metal. High sensibility of its mechanical properties to impurities (10 ppm is critical level for carbon!) has been severe restriction for experiments aimed to searching of inherent fracture mode for polycrystalline iridium. In present paper fracture behavior of high purity polycrystalline iridium and iridium, where grain boundaries (GBs) have been contaminated, are considered. Fine grained impurity-free metal exhibits 100% brittle transcrystalline fracture (BTF) and cracked GBs on the fracture surface and this is an inherent fracture mode of polycrystalline iridium. Re-crystallization in vacuum leads to appearance of BIF regions, whose total square can reach 100% of the fracture surface in coarse grain aggregates. Contaminated iridium mainly fails on grain boundaries, at that portion of BIF on the fracture surface (50 divided by 100%) does not depend on grain size. (C) 2004 Kluwer Academic Publishers.