Crystallographic data for the iron borate mineral, Hulsite1

The iron borate mineral, hulsite, from Brooks Mountain, Seward Peninsula, Alaska, was first described by Knopf and Schaller (1908). The chemical composition initially proposed for hulsite (Knopf and Schaller, 1908; Schaller, 1910) was later found to be incorrect (Schaller, written comm., 1955). The actual chemical composition is similar to that established for the ludwigite-vonsenite series of iron-magnesium-aluminum borates (Leonard and Vlisidis, 1960, 1961; Schaller and Vlisidis, 1961), i.e. (Fe,Mg)₂²⁺(Fe,Al)³⁺BO₃O₂. However, recent chemical studies by Schaller and Vlisidis (written comm., 1962) show that hulsite invariably contains tin (approximately 15 weight per cent SnO₂). Such sizeable amounts of tin have never been reported in analyses of members in the ludwigite-vonsenite series. Leonard, Hildebrand and Vlisidis (1962) state, “Tin is a minor constituent in quite a few members of the ludwigite-vonsenite series … and is a major constituent in the borate hulsite.” Samples of hulsite from Brooks Mountain were kindly provided by W. T. Schaller for x-ray diffraction examinations, and the present note records the results.