Abstract: A glass fiber composition comprises about 52-65 weight % SiO2; less than or equal to 4 weight % Al2O3; about 7-16 weight % Fe2O3; greater than 6 weight % and less than or equal to about 14 weight % R2O; about 6-25 weight % CaO; less than or equal to 10 weight % MgO; and about 10-25 weight % RO; wherein R2O represents alkali metal oxides and RO represents alkaline earth metal oxides. Preferably, the glass fiber composition has a liquidus temperature of less than 2350° F.; and a viscosity at a liquidus temperature of the glass fiber composition of greater than 500 poise; and fire resistant glass fiber formed from the glass fiber composition has a biodissolution rate of greater than 50 ng/cm2/hr.