Chrisstanleyite, Ag2Pd3Se4, is a selenide mineral that crystallizes in high saline, acidic hydrothermal solution at low temperatures as part of selenide vein inclusions in and alongside calcite veins. It tends to be found in assemblages of other selenides: jagueite, naumannite, fischesserite, oosterboschite, and tiemannite, and it is a solid solution mineral with jagueite Cu2Pd3Se4 in which it shares a unique crystal structure that has not been identified elsewhere (Paar et al. 1998; Nickel 2002; Paar et al. 2004). Chrisstanleyite and jagueite are unlike the other minerals of the selenide family as they do not have a sulfide analogue (Topa et al. 2006). First discovered by Werner Paar from a sample received from Hope's Nose, Torquay, Devon, England, chrisstanleyite has since been discovered in the Pilbara region of Western Australia and in El Chire, La Rioja, Argentina. Chrisstanleyite was named after the Deputy Head and Associate Keeper at the Department of Mineralogy at The Natural History Museum in London. Composition The chemical formula of chrisstanleyite is Ag2Pd3Se4 and contains trace amounts of Cu (Paar et al. 1998). Based on the sample received from Hope's Nose, England, Paar (1998) was able to utilize 7 grains in two polished sections to run 26 electron-microprobe analyses. The results of the analysis allowed Paar et al. (1998) to derive the average composition as (Ag2.01Cu0.02)Σ2.03Pd3.02Se3.95, or the ideal formula of Ag2Pd3Se4. The weight percent per element to create the ideal formula is Pd 37.52, Ag 25.36, Se 37.12, totaling 100% (Paar et al. 1998). The presence of Cu in the sample proved important as the discovery of chrisstanleyite in the Pilbara Region of Western Australia found intergrown with an unnamed Cu-dominant equivalent (Nickel 2002). In 2004, this unknown mineral was officially named jagueite, Cu2Pd3Se4, after being found in El Chire, Argentina (Paar et al. 2004) and has been identified to form a solid-solution with chrisstanleyite (Paar et al. 1998; Nickel 2002; Paar et al. 2004). Geologic Occurrence Chrisstanleyite occurs in selenide inclusions in and along calcite veins that cut through limestone (Paar et al. 2004). A selenide vein 10 cm below a calcite vein in Hope's Nose, where chrisstanleyite was initially identified, reflected a well-defined zoned sequence of minerals. The top of the sequence included native gold with small amounts of silver, while the middle layer consisted of palladian gold. The bottom layer consisted of selenide mineralization, primarily made of fischesserite (Paar et al. 1998). Chrisstanleyite