Crystallization Studies of Lunar Igneous Rocks: Crystal Structure of Synthetic Armalcolite

Science  04 Feb 1972:
Vol. 175, Issue 4021, pp. 521-523
DOI: 10.1126/science.175.4021.521


Crystals of armalcolite, Mg0.5Fe0.5Ti2O5, up to several millimeters in length have been grown from a glass initially having the composition of lunar rock 10017. A single-crystal x-ray study has confirmed that the crystals are isomorphous with pseudobrookite and has shown that the cations are strongly ordered, with the Ti4+ ions occupying the 8f sites and the Fe2+ and Mg2+ ions randomly distributed over the 4c sites. An examination of karrooite, MgTi2O5, has revealed a similar distribution of Mg2+ and Ti4+ ions. A reexamination of earlier x-ray and Mössbauer data for pseudobrookite, Fe2TiO5, has shown that it is more consistent with this type of ordering than with the inverse structure that has been generally assumed.