Abstract: A sand casting foundry composition reduces thermal defects that cause veining in metal parts cast from sand casting foundry shapes formed from the foundry composition. A plurality of foundry sand grains are mixed substantially uniformly with a plurality of shale particles, and a curable binder coats the sand grains and the shale particles to establish core and mold foundry shapes used to cast the metal part. Anti-veining capability occurs because the shale particles include mineral components which have an inherent characteristic of crystal structural collapse upon exposure to metallurgical temperatures, and the crystal structural collapse yields space which is consumed by thermal expansion of the sand grains in the foundry composition. This compensatory effect avoids the creation of mechanical forces and stresses within the foundry shape that cause cracks and fissures in the foundry shape that lead to veining.