Low cost, highly efficient thermoelectric materials for waste heat recovery applications can be made by combining the naturally occurring thermoelectric mineral tetrahedrite (Cu10Zn2As4S13) and the synthetic compound Cu12Sb4S13. To better utilize this material in waste heat harvesting applications, it is essential to characterize the material's mechanical properties including elastic modulus, hardness, and fracture toughness. In this study, powders of Cu10Zn2As4S13 were mixed with varying amounts of Cu12Sb4S13 and then densified by hot pressing. The room temperature mechanical properties were investigated as a function of (i) composition and (ii) ball milling time. Elastic moduli were measured using resonant ultrasound spectroscopy. Hardness and fracture toughness were determined by Vickers indentation technique.