GEOL 1121L Lab 4 (2026/2027) (PDF) | Rock Cycle & Igneous Rocks | GSU Geology

INSTANT PDF DOWNLOAD This GEOL 1121L Lab 4 Guide supports students in Introduction to Geology at Georgia State University (GSU). Lab 4 focuses on understanding the rock cycle and identifying igneous rocks based on texture, composition, and formation environment. This lab connects mineral knowledge to rock formation processes and tectonic settings. 1. The Rock Cycle The rock cycle explains how rocks change through time: Igneous → Sedimentary (weathering, erosion, deposition, lithification) Sedimentary → Metamorphic (heat and pressure) Metamorphic → Igneous (melting and crystallization) Any rock type can re-enter the cycle Key processes: Melting Cooling/crystallization Weathering & erosion Compaction & cementation Metamorphism 2. Igneous Rock Formation Igneous rocks form from magma or lava. Intrusive (Plutonic) Forms below surface Slow cooling Large crystals Extrusive (Volcanic) Forms at surface Rapid cooling Small or no crystals 3. Igneous Rock Textures Texture reflects cooling history: Phaneritic – coarse-grained, visible crystals Aphanitic – fine-grained Porphyritic – mixed crystal sizes Glassy – no crystals (obsidian) Vesicular – gas bubbles Pyroclastic – volcanic fragments