BUILDING HIGHER GEOLOGY CLASSIFICATION OF COMMON ROCKS A rock is a natural aggregate of minerals and non-mineral materials, such as fossils or glass. Rocks are the building blocks of the Earth s lithosphere (the crust and mantle, down to a depth of about 100 km), asthenosphere (a layer ranging in depth from about 100 to 250 km, and partially molten), mesosphere (from about 250 to 2900 km), and even part of the core (while the outer core is molten, the inner core is solid). Most rocks now exposed at the surface of the Earth formed in or on the continental or oceanic crust. Many rocks, formed beneath the surface and now exposed, were brought to the surface from great depths in the crust and in rare cases from the underlying mantle. There are three major classes of rocks: igneous rocks form by crystallization from a material called magma. There are two subclasses of igneous rock: volcanic and plutonic. sedimentary rocks form from material that has accumulated on the Earth s surface as a result of weathering and erosion, and organic material. metamorphic rocks form when a sedimentary or igneous rock is exposed to high pressure, high temperature, or both, deep below the surface of the Earth. beneath: al di sotto crust: crosta depth : profondità mantle: mantello molten: fuso subclasses: sottoclassi underlying: sottostante weathering: effetto degli elementi atmosferici 10 Complete the chart below. Classes of rocks Formed by/when 11 Answer the following questions. 1. What is a rock? 2. What are the Earth s layers? 3. Where did most rocks now exposed at the surface of the Earth form? 4. What are the two subclasses of igneous rocks? 5. What does the accumulated material on the Earth s surface consist of? 6. What happens when a sedimentary or igneous rock is exposed to high pressure, high temperature, or both, deep below the surface of the Earth? BIO AND MAN-MADE CONSTRUCTIONS 91