Rocks and The Rock Cycle

What is a Rock? A rock is a mixture of one or more minerals, glass, and sometimes, consolidated organic material (something that was once living). We classify rocks into 3 categories based on how they were formed: Igneous Sedimentary Metamorphic

Igneous Rocks The term igneous comes from the Latin word ignis, which means “fire” because early geologists often associated igneous rocks with fiery lava flows. They are formed from the crystallization of magma. Bowen’s reaction series tells us when and how the crystal form.

Bowen’s reaction Series

Igneous Rock Continue Igneous Rocks are the most common rock in the Earth’s crust. There are two types of Igneous rocks: Extrusive: fine-grained igneous rocks that cool quickly on Earth’s surface Intrusive: coarse-grained igneous rocks that cool slowly beneath Earth’s surface

Intrusive Extrusive

Classifying Igneous Rocks Once Igneous Rock have been classified has either intrusive or extrusive they are then classified by their mineral compositions. Mineral Composition: Felis: rocks such as granite are light-colored have high silica contents, and contain quartz and the feldspar orthoclase and plagioclase. Mafic: rocks such as gabbro are dark-colored, have lower silica contents, and are rich in iron and magnesium.

Classifying Continued Intermediate: is between felsic and mafic Ultramafic: such as peridotite and dunite, have low silica contents Texture: Extrusive rocks: Glassy or Fine-grained Intrusive Rocks: Coarse-grained or Very Coarse-grained Look at the following table:

Classifying Igneous Rock Table ExtrusiveFelsicIntermediateMaficUltramaficTexture ObsidianBasaltic Glass Glassy RhyoliteAndesiteBasaltFined grained IntrusiveGraniteDioriteGabbroPeridotiteDuniteCoarse - grained PegmatiteVery Coarse - grained

Sedimentary Rocks They are formed by sediments that have become cemented together. Sediments are pieces of solid material that have been deposited on Earth’s surface by wind, water, ice, gravity, or chemical precipitation. Sedimentary rocks can be formed from metamorphic, igneous, or other sedimentary rocks that have been broken down by weathering and erosion.

Sedimentary Continue Many components make it possible for Sedimentary rocks to form: Weathering is a set of physical and chemical processes that break rock into smaller pieces Erosion and Transport is the removal and movement of surface materials from one location to another. The four main agents of erosion are: wind, moving water, gravity, and glaciers. Deposition is when sediments are laid down on the ground or sink to the bottom of bodies of water Lithification is the physical and chemical processes that transform sediments into sedimentary rocks Cementation occurs when mineral growth cements grains together into solid rock.

Classifying Sedimentary Rocks The classification of sedimentary rocks is based on how they were formed. There are three main groups: Clastic: formed from the abundant deposits of loose sediments Organic: formed from the remains of once-living things Chemical: water evaporates and the minerals are left behind

Classifying Sedimentary Rock Table Rock TypeRock NameMethod of Formation Clastic Coarse grained Medium grained Fine grained Conglomerate or Breccia Sandstone Shale Lithification of clastic sediments Organic Calcium carbonate- shells Plant matter Limestone Coal Accumulation and lithification of remains of living things Chemical Calcite Halite Gypsum Limestone Rock Salt Rock Gypsum Precipitation of dissolved minerals from water

Metamorphic Rocks They are formed deep inside the Earth. Heat and pressure from the rock above flatten and bend the rock or even exchange atoms, forming new minerals. Metamorphic rocks have two categories: Foliated: wavy layers or bands of minerals form in the rock Non-Foliated: are composed of minerals that have blocky crystal shapes. Metamorphic rocks are created from sedimentary, igneous, and other metamorphic rocks

Metamorphic Rocks FoliatedNon-Foliated

The Rock Cycle The Rock Cycle helps us learn how each of the different rocks are formed. It is called a cycle because the rocks can travel in more than one path. The rocks of the Earth’s crust are constantly being recycled from one type to another. See below, the arrows represent the different processes that change rocks into there different types.

Rock Cycle diagram