In two samples of antigorite serpentinite from Sasaguri, Kyushu, Japan, we have found trace amounts of a NiFe-rich silicate whose atomic proportions in terms of the ratio of M to T cations match those of the fibrous MgFe-silicate hydrate balangeroite. Balangeroite in serpentinite at the type locality in Italy is not reported to contain Ni, whereas the balangeroite analogue from Japan has very little MgO. One sample from Japan is nickel-rich (up to 39 wt% NiO), and the other Fe-rich (up to 61 wt% total FeO). The Ni-rich sample appears to contain ~2 wt% Cl, and the Fe-rich sample contains up to 2.3 wt% P2O5. A wide miscibility gap in the ternary system Mg-Fe-Ni separates the Italian and Japanese minerals. Anhydrous microprobe totals are low, and we attribute this to a submicroscopic porosity, which is imaged by electron-beam scanning. Owing to its small grain-size (<25 μm) and very low modal abundance, our identification is as yet not confirmed by physical methods, such as XRD or micro-Raman spectroscopy.

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