The attempts made to understand and quantify the relationship between rock texture and engineering properties have been accompanied by some ambiguities and uncertainties, and the majority of the approaches, though focusing on particular rock types, have not been so successful for even the same rock types from other regions. This study, therefore, was aimed to investigate the relationship between the texture and strength properties of a wide range of crystalline igneous rocks along with more aspects of textural analysis. For this purpose, fifteen fresh samples of crystalline igneous rocks belonging to the stone quarries of the NW Iran were collected and subjected to compressive and tensile strength tests (UCS and BTS). Thin sections of the samples were used to prepare the full mosaic image layers in three different optical conditions. About 18,000 mineral grains were manually traced on the processed images and the obtained vector data was used for the quantification of various textural parameters including size metrics, shape descriptors, microfabric indices and mineral content. Different phase considerations (full-phasic, monophasic, multiphasic and phase-ratio) were applied to derive the textural characteristics of the individual and multiple minerals and their proportional ratio. Finally, simple linear regression analysis was performed to evaluate the relationship between the texture and strength properties. The results indicated that the newly developed quartz to feldspar size ratio (QFSR) indicator was the only textural parameter that could be significantly correlated with both compressive and tensile strength in a wide range of rock types. The results also highlighted the fact that the role of quartz and feldspar encountered with different rock failure mechanisms could be different; In fact, the tensile strength was obviously affected by the size and content of K-feldspar, while the compressive strength showed a more complicated mechanism and seemed to be controlled by the interference effects of plagioclase and quartz textural properties. Furthermore, the study indicated that the influence of grain size on the rock strength was more important than the grain shape or mineral content.

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