Micro-textural effects on crack initiation and crack propagation of andesitic rocks

The synthesis of mechanical, mineralogical, petrographic and microstructural data suggests that both the crack initiation threshold and peak strength are influenced by the ratio of the area of fine grain groundmass (grains smaller than 200 μm) to amphibole and plagioclase phenocrysts. In addition σCI and UCS decrease with an increasing normalized area of biotite phenocryst.