Method for manufacturing carrier granules. The method forms a mixture comprising fibers, mineral filler, and binder. The mixture contains 32-48 weight-% wood fibers having a bulk density of less than 20 pounds per cubic foot, at least 35 weight-% of which fibers are retained on a 50-Mesh U.S. Sieve Series screen. The fibers have a moisture content of less than 15 weight-%. The mixture also contains 52-65 weight-% mineral filler having a moisture content of less than 12 weight-%. In addition, the mixture contains 3-7 weight-% binder. The mixture is agglomerated by conditioning and agglomerating it in a pin mixer to form small particles followed by agglomerating it in a disc or pan pelletizer to form substantially spherical granules. The method then dries the granules to a moisture content of less than about 5 weight-%, and screens the granules to select granules that pass through a 10-Mesh U.S. Pat. No. Sieve Series screen but are retained on a 40-Mesh U.S. Pat. No. Sieve Series screen. The carrier granules have a bulk density of less than 40 pounds per cubic foot and a Resistance to Attrition of at least 95%.