AbstractMeasures of the differential relief of adjacent feldspar and pyroxene grains provide the first clear negative correlation of Schmidt hammer rebound (R‐) values and degree of weathering. However, weathering and roughness are intimately related, so the latter cannot be seen simply as a source of error limiting the utility of the Schmidt hammer. Only where surfaces had similar textures prior to weathering can R‐values be compared directly. Even where surface texture is well controlled, differences in R‐values should be viewed critically rather than assigned indiscriminately to differences in degree of weathering.