Under the low temperature and pressure conditions of Earth's upper lithosphere, silicate rock responds to large strains by brittle fracture. The mechanism of brittle behavior is by the propagation of cracks, which may occur on all scales. We begin by studying this form of deformation, which is fundamental to the topics that follow.

Theoretical concepts

Historical

Understanding the basic strength properties of rock has been a practical pursuit since ancient times, both because of the importance of mining and because rock was the principal building material. The crafting of stone tools required an intuitive grasp of crack propagation, and mining, quarrying, and sculpture are trades that require an intimate knowledge of the mechanical properties of rock. The layout and excavation of quarries, for example, is a centuries-old art that relies on the recognition and exploitation of preferred splitting directions in order to maximize efficiency and yield. One of the principal properties of brittle solids is that their strength in tension is much less than their strength in compression. This led, in architecture, to the development of fully compressional structures through the use of arches, domes, and flying buttresses.

Rock was one of the first materials for which strength was studied with scientific scrutiny because of its early importance as an engineering material. By the end of the nineteenth century the macroscopic phenomenology of rock fracture had been put on a scientific basis.