What is a Rock? A rock is a: –N–N–N–Naturally formed, –C–C–C–Consolidated material, –C–C–C–Composed of grains of one or more minerals.

Some Rocks

Types of Common Rocks There are three types of common rocks:There are three types of common rocks: –Igneous rock –Sedimentary rock –Metamorphic rock

Igneous Rock Igneous rocks form from the solidification of magma.Igneous rocks form from the solidification of magma. –Ex: pumice, obsidian

Identifying Igneous Rocks igneous rockWhere the igneous rock forms in the crust shapes their composition so igneous rocks are identified by their texture. –Extrusive rocks fine-grained. –Extrusive rocks form at or near the surface and are fine-grained. –Intrusive rocks coarse-grained –Intrusive rocks form below the surface and are coarse-grained.

Basalt: Igneous – Extrusive, Fine-grained

Granite: Igneous – Intrusive, Coarse-grained

Igneous Rock Features: Felsic Felsic rocks light in colorFelsic rocks are rich in potassium feldspar and quartz and are light in color. granite –Example is the granite family of rocks. Felsic rocks continentsFelsic rocks are most common in the continents.

Felsic Igneous Rocks

Igneous Rock Features: Mafic Mafic rocks are rich in d dd dark plagioclase feldspar and pyroxene. –E–Example the g gg gabbro family of rocks. Mafic rocks are more common in the ocean basins.

Mafic Igneous Rocks Basalt

Igneous Identification Some igneous rocks have holes in them that formed during the cooling of the magma. These types are said to bevesicularSome igneous rocks have holes in them that formed during the cooling of the magma. These types are said to be vesicular.

Igneous Rocks

Structure of Igneous Rocks ShieldCinder Cone lava plateausShield and Cinder Cone volcanoes will erupt and create lava flows, and lava plateaus, that form igneous rocks. plutonsWhen magma does not erupt but instead forces its way up through cracks and faults it produces large masses of intrusive rock called plutons.

Shield (Etna) and Cinder Cone (Paracutin)

Plutons Plutons are classified according to size: Sills are slabs of igneous rock parallel to the rocks they intrude; Dikes are slabs of igneous rock that cut across the rock layers they intrude; A l ll laccollith forms between two rock layers, bulging up to form a dome; A b bb batholith is the largest intrusion and they form the core of many mountain ranges. When a volcano erodes the harder v vv volcanic neck is often left behind.

Devil’s Tower is the result of igneous rock that was underground until all the weaker surrounding rock was eroded