Chrisstanleyite, Ag₂Pd₃Se₄, is a new mineral from gold-bearing carbonate veins in Middle Devonian limestones at Hope's Nose, Torquay, Devon, England. It is associated with palladian and argentian gold, fischesserite, clausthalite, eucairite, tiemannite, umangite, a Pd arsenide-antimonide (possibly mertieite II), cerussite, calcite and bromian chlorargyrite. Also present in the assemblage is a phase similar to oosterboschite, and two unknown minerals with the compositions, PdSe₂ and HgPd₂Se₃. Chrisstanleyite occurs as composite grains of anhedral crystals ranging from a few µm to several hundred µm in size. It is opaque, has a metallic lustre and a black streak, VHN₁₀₀ ranges from 371–421, mean 395 kp/mm² (15 indentations), roughly approximating to a Mohs hardness of 5. D_calc = 8.308 g/cm³ for the ideal formula with Z = 2. In plane-polarised reflected light, the mineral is very slightly pleochroic from very light buff to slightly grey-green buff; is weakly bireflectant and has no internal reflections. Bireflectance is weak to moderate (higher in oil). Anisotropy is moderate and rotation tints vary from rose-brown to grey-green to pale bluish grey to dark steel-blue. Polysynthetic twinning is characteristic of the mineral. Reflectance spectra and colour values are tabulated. Very little variation was noted in eleven electron-microprobe analyses on five grains, the mean is: Ag 25.3, Cu 0.17, Pd 37.5, Se 36.4, total 99.37 wt.%. The empirical formula (on the basis of ΣM + Se = 9) is (Ag_2.01Cu_0.02)_Σ2.03 Pd_3.02Se_3.95, ideally Ag₂Pd₃Se₄. Chrisstanleyite is monoclinic, a 6.350(6), b 10.387(4), c 5.683(3) Å, β 114.90(5)° space group P2₁/m (11) or P2₁(4). The five strongest X-ray powder-diffraction lines [d in Å (I)(hkl)] are: 2.742 (100) (−121), 2.688 (80) (−221), 2.367 (50) (140), 1.956 (100) (−321,150) and 1.829 (30) (−321,042). The name is in honour of Dr Chris J. Stanley of The Natural History Museum in London. The mineral and its name have been approved by the Commission on New Minerals and Mineral Names of the International Mineralogical Association.