gen-define-igneous-versus-sedimentary-versus-metamorphic-rock-an-d1ff

Define igneous versus sedimentary versus metamorphic rock and give one short worked example.

# Three Types of Rocks ## **Igneous Rock** Forms from cooling and solidification of molten material (magma or lava). - **Intrusive**: Cools slowly underground → large crystals (e.g., granite) - **Extrusive**: Cools quickly at surface → small crystals (e.g., basalt) ## **Sedimentary Rock** Forms from accumulation and cementation of sediments (rock fragments, minerals, organic material). - Layers deposited over time - Often contains fossils - Examples: sandstone, limestone, shale ## **Metamorphic Rock** Forms when existing rocks are transformed by heat and/or pressure (without melting). - Original rock structure changes - New minerals may form - Examples: marble, slate, schist --- ## **Worked Example: The Life Story of a Sandstone** 1. **Starting as sedimentary**: Sand grains accumulate on an ancient beach and cement together → **sandstone** forms 2. **Becoming metamorphic**: Tectonic plates collide, burying the sandstone deep underground. Intense heat (300°C) and pressure compress it, recrystallizing the grains → transforms into **quartzite** 3. **Becoming igneous**: Continued subduction takes the quartzite even deeper where temperatures exceed 900°C. It melts completely into magma, then rises and cools → crystallizes as **granite** This illustrates the **rock cycle**: any rock type can transform into any other type!