The Pseudobrookite Group: Crystal Chemical Features of the Armalcolite Fe²⁺ Analogue

Abstract

The crystal structure of a potentially new mineral, the Fe²⁺-dominant analogue of armalcolite with the idealized formula Fe²⁺Ti₂O₅ has been solved. The sample studied originates from a pneumatolytic association related to the lamproite complex of SE Spain. The mineral is orthorhombic, space group Cmcm, the unit-cell parameters are a = 3.7325(1) Å, b = 9.7649(4) Å, c = 9.9902(3) Å, V = 364.12(2) ų. The crystal-chemical formula ${{^{M}}^{1}}{{({\text{M}}{{{\text{g}}}_{{0.19}}}{\text{Fe}}_{{0.25}}^{{2 + }}{\text{Fe}}_{{0.26}}^{{3 + }}{\text{T}}{{{\text{i}}}_{{0.30}}})}^{{2.86 + }}}$${{{{[}^{M}}^{2}{{({\text{T}}{{{\text{i}}}_{{0.65}}}{\text{Fe}}_{{0.27}}^{{3 + }}{\text{Fe}}_{{0.08}}^{{2 + }})}^{{3.57 + }}}]}_{2}}{{{\text{O}}}_{5}}$ (Z = 4) is in good agreement with the chemical composition of the mineral.