The effect of F on the density of haplogranite melt
The densities and thermal expansivities of F-bearing haplogranitic glasses and liquids\nhave been investigated using a combination of scanning calorimetry and dilatometry.\nF2O-1 reduces the density of haplogranitic liquids (at 750 \xb0C) from 2.295 + 0.006 g/cm3\nto 2.261 + 0.005 g/cm3 with the addition of 4.55 wt% F (0.33% per wt% of F added). The\nexpansivities of the liquids increase with the addition of F2O-1 from 29.9 +- 3.0 x l0 -6/\xb0C to 53.1 +- 1.4 x l0 -6/\xb0C (at 750\xb0C).\nDensities have been converted into molar volumes based on the haplogranite and F2O-1\ncomponents. The partial molar volume of F2O-1 has been calculated at 750\xb0C to be 14.2\n+- 1.3 cm3/mol in these melts. This value is close to the molar volume per O for several\ncomponents of silicate melts. F and O have similar ionic and covalent radii, and thus the\nsubstitution of two F for one O yields approximately the volume change expected, assuming\nno secondaryc onsequencesfo r the averagec oordination number of cations. This is\ndespite evidence from quenched melts that [6]Al exists in these compositions.\nF is significantly more effective (per wt% added) than B2O3 in reducing the density of\nhaplogranitic melt. The effect of F on density reported here should complement the viscosity-\nreducing effect of F2O-1 on granitic melts in significantly acceleratingg ravity-driven\nprocesses of crystal-melt fractionation in F-rich igneous systems.