Cobaltoan staurolite from Zambia

A cobalt-blue staurolite, containing 2.52 % CoO, is described from a locality east of Lusaka, Zambia. This locality is believed to be identical with that of lusakite described by Skerl and Bannister (1934). The mineral is pseudo-orthorhombic, with a = 7.876(1), b = 16.592(1), c = 5.652(1) Å, β = 90,00(2)°, a : b : c = 0.475 : 1 : 0.341, V = 738.63(14) ų, Z = 2 ; D(m) = 3.737, D(x) = 3.758 g/cm³. It forms anhedral to subhedral grains up to 0.6 x 1.0 x 1.7 mm in size, which are associated with major magnetite (1.6 % CoO) and hematite. Other associated minerals include quartz, kyanite, ilmenite (2.3 % CoO), rutile, cobaltoan högbomite-4H (6.52 % CoO), cordierite (0.09 % CoO), sillimanite, Mg-chlorite, monazite, linnaeite, and pentlandite. — It is proposed that the name lusakite be retained for the cobaltoan analogue of staurolite with Co > Fe, Mg..