A second world occurrence for bulachite, Al-2(AsO4)(OH)(3). 3H(2)O, has bee
n found in a few specimens collected on a mine dump from old workings in an
arsenopyrite lens in south Sardinia (Italy). The mineral occurs as sparse,
whitish, satiny. crumbly polycrystalline aggregates on mansfieldite and go
ethite encrusting quartzite clasts, Bulachite is intimately mixed with kaol
inite, illite and an amorphous allophane-like phase, and with minor amounts
of quartz and Fe3+ oxyhydrorides, Bulachite crystals occur as very slender
, curved fibres (about 250 nm in diameter and up to 150 mum long) aggregate
d into radial or sub-parallel groups. A least-squares unit-cell refinement
of 34 reflections from X-ray powder diffraction analysis gave the following
results for an orthorhombic cell: a = 15.53(3) Angstrom, b = 17.79(3) Angs
trom, c = 7.01(1) Angstrom, V = 1936(4) Angstrom (3).