Deformation and microhardness studies on natural apophyllite crystals

Microhardness testing of three different planes of natural apophyllite crystals is reported. Variation of Vicker's microhardness value H_v with applied load ranging from 10–100 g indicates two distinct regions. In the low load region (10–70 g) H_v increases with load till it attains maximum value and then decreases thereafter. This variation is explained qualitatively in terms of depth of penetration of the indentor. Variation of orientation of the indentor w.r.t. each of the (100) and (111) planes indicates microhardness anisotropy.