Figure 12From: Water-melt interaction in hydrous magmatic systems at high temperature and pressure Distribution of NBO/T values for melts of some common igneous rocks. The inset shows the relationship between average values of SiO2 + Al2O3 of rhyolite (SiO2 + Al2O3 = 85.4 wt%), phonolite (SiO2 + Al2O3 = 79.5 wt%), dacite (SiO2 + Al2O3 = 80.8 wt%), andesite (SiO2 + Al2O3 = 74.4 wt%), and tholeiite (SiO2 + Al2O3 = 65.1 wt%) melts (rock composition data from http://Earthchem.org used as described by Mysen and Richet 2005, ch. 17).Back to article page