What is the difference between an igneous rock and a sedimentary rock?
Sedimentary rock is one of the three main rock groups (along with igneous and metamorphic rocks) and is formed in three main ways—by the deposition of the weathered remains of other rocks (known as ‘clastic’ sedimentary rocks); by the deposition of the results of biogenic activity; and by precipitation from solution. Sedimentary rocks include common types such as chalk, limestone, sandstone, clay and shale. Sedimentary rocks cover 75% of the Earth’s surface. Four basic processes are involved in the formation of a clastic sedimentary rock: weathering (erosion), transportation, deposition and compaction. Igneous rocks are formed when molten rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This magma can be derived from partial melts of pre-existing rocks in either the Earth’s mantle or crust. The melting is caused by one or more of the following processes — an incre
