Lithium-free high modulus fiberglass composition

A lithium-free glass composition comprising:

• SiO2 in an amount from 50 to 57% by weight;
• Al2O3 in an amount from 18 to 22% by weight;
• CaO in an amount less than 10% by weight;
• and
• MgO in an amount from greater than 12% by weight to less than 15% by weight, wherein a total concentration of CaO+MgO is between 20% by weight and less than 25% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the glass composition satisfies the following:
• a ratio C1 (C1=SiO2/(MgO+CaO)) of 2.3-2.7;
• and
• a ratio C2 (C2=MgO/CaO) of at least 1.3, wherein the glass composition has a fiberizing temperature no greater than 1,300° C.

A glass fiber formed from a glass composition comprising:

• SiO2 in an amount from 50 to 57% by weight;
• Al2O3 in an amount from 18 to 22% by weight;
• CaO in an amount from 7 to 12% by weight;
• MgO in an amount from 11.5 to 15% by weight;
• Na2O in an amount from 0.05 to 0.5% by weight;
• ZrO2 in an amount from 0 to 5% by weight;
• and
• Li2O in an amount less than 0.5% by weight, expressed as percentages by weight based on the weight of the entire composition, wherein the glass composition satisfies the following:
• a ratio C1 (C1=SiO2/(MgO+CaO)) of 2.3-2.7;
• and
• a ratio C2 (C2=MgO/CaO) of at least 1.3, wherein the glass composition has a fiberizing temperature no greater than 1,300° C., and wherein the glass fiber has a Young's modulus of at least 90 GPa.