Fracture behavior of high pure polycrystalline iridium and iridium, where grain boundaries have been contaminated, is considered. Mixture of brittle transcrystalline and brittle intercrystalline fracture, where portion of the last depends on grain size, is the inherent fracture mode of this refractory fcc-metal (T_(melt) = 2443 deg C). 100 percent brittle intercrystalline fracture of fine grain aggregate means impurities induced fracture of iridium. At that high pure metal exhibits poor plasticity and brittle fracture under tensile stress only, while contaminated polycrystalline one is unworkable material. Another word "inherent brittleness" is specific property of iridium, which contrasts with brittle fracture behavior of crystal when it could not be deformable solid. Physical mechanisms of brittle transcrystalline fracture and grain boundaries brittleness in polycrystalline iridium are discussed.
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