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Rocks: Mineral Mixtures th 8 Grade Section 1: Understanding Rock • What exactly is rock? –A solid mixture of crystals of one or more minerals, that range in all sizes from pebbles to formations that are thousands of kilometers long. The Value of Rock • Rock is an important natural resource. • Used by early humans to make tools such as hammers, spears, knives, and scrapers. • Used for centuries to make buildings, roads, and monuments. • Certain types of rocks have helped build ancient and modern civilizations. • Rock study has helped scientists to discover the history of life on Earth. Machu Picchu, Peru 600 A.D. Ancient Civilization Rock Structure Fossils • Help provide information of life forms that lived thousands of years ago. The Rock Cycle • Rocks in the Earth’s crust are constantly changing shape and composition. • The way the rock forms determines the type of rock that it is. • The three main types of rocks are: igneous, sedimentary, and metamorphic.