The structure of the mineral schultenite, PbHAsO4, has been studied using pulsed neutron single crystal diffraction. The low-temperature, low-symmetry structure is found to exhibit substantial ordering of the hydrogen atom onto one of two possible sites, which are equally occupied in the high-temperature phase above 313 K. The occupancies found at low temperature agree well with the normal behaviour for such a hydrogen ordering phase transition in this type of material. In addition the heavy atom lattice distortion has been characterised as a function of temperature and found to follow broadly the pattern of hydrogen ordering. Higher-temperature measurements at and above the phase transition confirm the high symmetry nature of the structure in this region, with no significant distortions from this within the resolution of the present data.

Schultenite, PbHAsO4, known only from Tsumeb, Namibia, has been identified from a second occurrence: near North Bend, King County, Washington, USA. It occurs as euhedral crystals in a quartz-arsenopyrite-galena vein. It has a measured density of 6.07(3) g/cm3 and a calculated density of 6.079(4) g/cm3. The white to colourless crystals have a white streak, adamantine lustre, and fluoresce dull yellow under long wave ultraviolet light. Schultenite is monoclinic. Pa or P2/a; the unit cell parameters refined from the X-ray powder diffraction data are: a 5.827(3), b 6.743(3), c 4.847(3) Å, β 95.34(5)°; V 189.6(1) Å3; Z = 2; a:b:c = 0.8642:1:0.7188. The forms {010}, {001}, and {3̄22} were observed on the Washington schultenite crystals.