THE CRYSTAL CHEMISTRY OF THE KORNERUPINE-PRISMATINE SERIES. IV. COMPLETE CHEMICAL FORMULAE FROM ELECTRON-MICROPROBE DATA AND X-RAY POWDER DIFFRACTION

Abstract

A procedure is developed whereby complete chemical formulae and chemical compositions of kornerupine may be derived from electron-microprobe data and unit-cell dimensions. The boron content (as B in apfu ) can be expressed as a linear function of the a and c cell parameters and the Al 2 O 3 and FeO contents (as wt.% oxide). The content of ferric iron (as Fe 3+ in apfu ) can be expressed as a linear function of the B content (as B apfu ) and the Al 2 O 3 and FeO contents (as wt.% oxide). The hydrogen content (in H apfu ) can be expressed as 1 – F ( apfu ). Standard errors of estimates for B and Fe 3+ are both 0.05 apfu .