Sodic-calcic and alkali amphiboles from benmoreitic members of the Igaliko Dyke Swarm contain up to 4.13 wt. % ZrO₂. It is proposed that Zr enters the amphiboles by a coupled substitution of ZrC4++AlT3+⇌FeC3++SiT4+ (where C = octahedral site and T = tetrahedral site) to produce the richest Zr-bearing amphiboles so far identified, with compositions ranging up to K 0.48 Na 2.30 Ca 0.32 [ Ti 0.00 Fe 0.38 3+ Fe 3.95 2+ Mn 0.14 Mg 0.25 Zr 0.33 ] Si 7.58 Al 0.36 O 22 (OH) 2 These amphiboles crystallize at a late stage from magmas which were Zr-rich, highly peralkaline and hydrous, with an f_o2 close to the synthetic QMF buffer. The incorporation of Zr in to the amphibole is a consequence of the failure of other Zr-bearing phases (such as zircon, baddeleyite, eudialyte) to crystallize.