3 Groups of Rocks Igneous intrusive extrusive Sedimentary

3 Groups of Rocks • Igneous : intrusive & extrusive • Sedimentary : clastic, organic, chemical • Metamorphic : foliated & nonfoliated

How are Igneous Rock Classified ? • Origin • Texture • Mineral composition

ORIGIN • Extrusive : formed from lava that erupted onto Earth’s surface. Basalt is the most common example. • Intrusive : formed when magma hardened beneath Earth’s surface. Granite is the most abundant intrusive rock in the continental crust.

Texture • Fine Grain : rapid cooling with small crystals ex. Rhyolite • Coarse Grain : slow cooling with large crystals ex. Gabbro • Glassy : fastest cooling with no crystals ex. Obsidian • Porphyritic : large crystals surrounded by fine grain crystals ex. Porphyry

Mineral Composition • Low silica content results in dark colored rocks ex. Basaltic – Andesite extrusive igneous • High silica content results in light colored rocks ex. Grantic – Gniess intrusive igneous

Sedimentary Rocks

How do Sedimentary Rock Form ? • Weathering and Erosion • Deposition • Compaction • Cementation

3 Groups of Sedimentary Rocks • Clastic : forms when rock fragments are squeezed together • Ex. Shale • Ex. Sandstone • Ex. Conglomerate

• Organic : forms from the remains of plants and animals • Ex. Coal • Ex. Limestone

• Chemical : forms when minerals that are dissolved in a solution crystallize • Ex. Halite • Ex. Gypsum

Metamorphic Rock • Forms from other rocks deep beneath the Earth’s surface which are under the influence of Heat & Pressure • Foliated : has layers • Nonfoliated : no layers

Foliated Metamorphic • Slate • Gneiss • Schist

Nonfoliated Metamorphic • Quartzite • Marble • Soapstone

The Rock Cycle