Crystal chemistry of clinopyroxene and its petrogenetic significance: a new approach

A synthesis and interpretation of the crystal chemistry of 156 clinopyroxenes from volcanic and mantle parageneses are attempted. These are based on actual site occupancy and polyhedral configurations obtained by means of a methodology which combines single crystal X-ray structural refinement and electron probe microanalysis of the same crystal (Dal Negro et al., 1982). Specific intracrystalline constraints characteristic of distinct magmatic environments have emerged as important petrological indicators. Possible physico-chemical factors responsible for the configurational imprint of the clinopyroxene are examined in detail. fO2 in the parentalmagma and hydrostatic pressure are crucial in the understand ing of the clinopytoxene response to different magmatic regimes. Mg-Fe2+ order-disorder relationships are configuration-dependent and pressure-sensitive. Conventional chemical data on clinopyroxene should be complemented by intracrystalline configuration data in order to understand the nature of the clinopyroxene as a useful genetic indicator.