Britannica Educational Publishing 
Rocks [PDF ebook] 

Often concealing millennia worth of Earth’s history, rocks seem to project an impression of durability and permanence that belies their transformation over time. Seen in all shapes and sizes and found in many of the planet’s ecosystems, rocks have been subject to various natural forces that have affected such attributes as their elasticity, strength, and ductility (that is, their ability to be fashioned into a new form). The general properties as well as the three major categories of rock-igneous, sedimentary, and metamorphic-are all examined in depth in this penetrating volume.