Rocks and the Rock Cycle Chapter 14

How Igneous Rocks Form Forms when molten rock cools and hardens. Can form below the Earth’s surface from magma – Intrusive igneous rocks. Can form on the surface from lava that erupts from a volcano – Extrusive igneous rock. Changes forms by melting and cooling.

Composition of Igneous Rocks The substances making up the molten rock determine the composition of igneous rock. The difference in the color depends on the composition of igneous rock. Rocks that contain silicon, aluminum, sodium, & potassium are lighter in color & less dense. Rocks that contain iron, magnesium, & calcium are darker in color & more dense.

Texture of Igneous Rock The amount of time it takes for the molten rock to cool determines the rock’s texture. The more time the crystals have to grow, the coarser the texture of the rock. Igneous rocks that form at the surface have fine grained texture. Igneous rocks that form below the surface have a coarse grained texture.

Examples of Igneous Rocks Granite Obsidian Basalt Gabbro Pematite Diorite Perilotite Rhyolite Pumice Andesite Scoria

How Sedimentary Rocks Form Forms from layers of sediment that are compacted and cemented together. Forms at or near the Earth’s surface. Forms layers called strata. Changes forms by weathering and erosion.

Composition of Sedimentary Rock Clastic- rock or mineral fragments stick together Chemical- when minerals crystallize out of a solution Organic- forms from the remains of organisms

Texture of Sedimentary Rock Strata differ in kind, color, and size of sediment. There are fine-grained, medium-grained, and coarse-grained texture.

Examples of Sedimentary Rock Sandstone Conglomerate Limestone Clay Siltstone Mudstone Arkose Shales Breccia

How Metamorphic Rock Forms Takes place mostly at depths greater than 2 km. Changes forms by heat and pressure. Some contain parallel bands of minerals.

Composition of Metamorphic Rock Formed from minerals at certain depths within the Earth.

Texture of Metamorphic Rock Foliated- consists of minerals that are aligned Nonfoliated- does not appear to have any regular pattern; contains only one or just a few minerals

Examples of Metamorphic Rock Slate Phyllite Schist Gneiss Marble Quartzite Hornfels

The Rock Cycle The rocks of the Earth’s crust are constantly changing. Rock changes its shape and composition in a variety of ways. The way rock forms determines what type of rock it is. The rock cycle is the process by which one rock type changes into another.