Yukonite, a rare hydrated Ca-Fe arsenate, occurs at Redziny (Sudetes, Poland) in a zone of weathering of a polymetallic mineralization in dolomitic marbles. Brittle, very fine-grained, gel-like aggregates of the -mineral are dark brownish or dark brown, sometimes with a noticeable violet tint. In smaller fragments it is often translucent, purple reddish, with smooth surfaces and vitreous lustre. Yukonite originated during weathering of arsenopyrite, relics of which are sometimes present within the yukonite aggregates. It is accompanied by other arsenates (pharmacosiderite, conichalcite), arsenopyrite, quartz and talc. Yukonite has been identified by X-ray diffraction and electron-microprobe analysis.