K-POOR TITANIAN FLUOR-RICHTERITE FROM NEAR NULLAGINE, WESTERN-AUSTRALIA

Strongly zoned amphibole formed of titanian fluor-richterite cores wit h 2.24% TiO2 and margins of titanian ferro-richterite with 6.65% TiO, is described from a basaltic andesite. The cores are richer in F, Al, Mg, and Ca than the edges, which are richer in OH, Ti, Fe, Na, and K. Similar sodic-calcic amphiboles are widely known to appear in lamproit es, but typically they contain 5% or more K2O, whereas the present sam ple reaches a maximum of 1.18% K2O at the margin. As is characteristic of titanian potassium richterite, there is Ti in tetrahedral coordina tion and a pink to yellow pleochroism. Ba, Sr, Li, B, Cl, Be, Nb, La, Ce, Pr, Y, V, and Zr contents are given. Zoned augite with Ca42Mg42Fe1 6 cores and Ca43Mg35Fe22 rims is also present, plus chloritic material and feldspar.