Chapter 3 Rocks A rock is a solid mass of minerals or mineral-like materials. The three major types of rock are igneous, sedimentary, and metamorphic. The rock cycle summarizes how each of these rock types form and also describes how they can be transformed from one type to another.

Section 3.1 The Rock Cycle The parent material for all rock is magma. Magma is molten rock underground, and if it reaches the surface it is called lava. Igneous Rocks form from cooled magma or lava. Sedimentary Rocks form from layers of weathered, eroded, and deposited sediment. Metamorphic Rocks form when preexisting rocks are altered by pressure, heat, and/or fluids. The processes of melting, cooling, weathering, erosion, deposition, and lithification can transform any type or rock into another.

Section 3.2 Igneous Rocks Igneous rocks form when magma or lava cools. Igneous rocks formed from magma beneath Earth’s surface are known as intrusive igneous rocks. Granite is an example. It makes up the rocks of many continents.

Classification of Igneous Rocks Texture and Composition together are used to classify igneous rocks. Intrusive igneous rocks cool slowly from magma, because they are insulated inside the Earth. This results in the formation of large crystals, also known as coarse grains. Granite, Gabbro, and Diorite are examples.

Classification of Igneous Rocks Extrusive igneous rocks cool quickly from lava, because they are exposed to air and water at the Earth’s surface. This results in little or no crystals, also known as fine grains. Basalt and Rhyolite are examples. Obsidian has no crystals, also known as volcanic glass.

Igneous Rocks Key words to look for on SOL: melting, lava, magma, intrusive, extrusive, crystals, or grains. Examples: basalt, granite, gabbro, diorite, andesite, and rhyolite. Basalt is an extrusive igneous, fine grained rock that forms most of the oceanic crust. Granite is an intrusive igneous, coarse grained rock that forms most of the continental crust.

Section 3.3 Sedimentary Rocks Sedimentary rocks form when larger rocks are broken down into smaller pieces called sediments by the process of weathering. Mechanical weathering is the physical breakdown of rock. Ice wedging is a type of mechanical weathering. Chemical weathering is when minerals in rock change into new substances. Carbonation is a type of chemical weathering that dissolves Limestone to form caverns and caves. Erosion is the picking up and carrying away of sediments. Deposition is when erosion stops and sediments “pile up” or deposit.

Formation of Sedimentary Rocks After sediments have been deposited by deposition, compaction or cementation can occur. Compaction is a process that squeezes, or compacts, sediments. Cementation takes place when dissolved minerals are deposited in the tiny spaces among sediments, binding them into a solid mass. Sedimentary rocks form in layers known as strata.

Classification of Sedimentary Rock into 3 groups Clastic Sedimentary – rocks made from a sediments that come from preexisting rock. Conglomerates have large rounded sediments. Breccias have large angular sediments.

Classification of Sedimentary Rock into 3 groups Chemical Sedimentary Rocks – rocks made of dissolved sediments that precipitate, or separate, directly from water. Precipitation usually occurs when water evaporates, leaving once dissolved solids behind. Rock salt is formed when halite precipitates from seawater. Chemical Limestone forms when calcite precipitates directly from water. Chemical Limestone Rock Salt

Classification of Sedimentary Rock into 3 groups Biochemical Sedimentary Rocks (organic sedimentary rocks) – rocks made of sediments derived from biological processes. Organic Limestone forms from the shells of tiny marine organisms. Coal is also an organic sedimentary rock. Coal is made primarily of the remains of swamp plants. Organic Limestone and Coal are both abundantly found in Virginia. Organic Limestone (Coquina) Coal

Sedimentary Rock Features ALL FOSSILS ARE FOUND IN SEDIMENTARY ROCKS!!!!! Strata – layers of sedimentary rock. Each layer records a period of deposition. Ripple marks – indicate that the rock formed in the presence of water. Mud cracks – indicate that rock formed as sediments were drying.

Key Words on SOL for Sedimentary Rock Stata, or layers, weathering, erosion, deposition, compaction, cementation, clastic, chemical, organic, sediments, conglomerate, breccia, and FOSSILS! Examples include : Coal, Limestone, Sandstone, Rock Salt, Shale, Dolomite, and Gypsum.

Section 3.4 Metamorphic Rocks Metamorphism is the transformation of preexisting rock by heat and pressure. The newly formed metamorphic rock tends to be very different from the parent rock. Most often occurs deep in the Earth’s crust where heat and pressure are higher. There are two types of metamorphism. Contact Metamorphism occurs when intruding magma causes localized areas of elevated temperature that alter rock. Regional Metamorphism occurs over large areas of Earth’s crust, usually during mountain building, and is associated with very high temperatures and pressures. It occurs near plate boundaries.

Agents of Metamorphism The agents of metamorphism are heat, pressure, and fluids. Heat – the most important agent. Heat provides the energy for chemical reactions. Pressure – there are two types. Confining pressure occurs equally in all directions making the rocks more compact and dense. Directed pressure is greater in one direction than others. It is associated with mountain building and causes dramatic folds in rocks. Fluids – hydrothermal solutions promote recrystallization by dissolving original minerals and depositing new ones, changing the mineral composition of the rock.

Classification of Metamorphic Rock Foliated metamorphic rocks are banded or layered. They contain minerals that are oriented perpendicular to the direction of greatest pressure. Gneiss pictured to the right is an example Nonfoliated metamorphic rocks have no bands or layers. They formed under high temperatures and even, confining pressure. Examples include Marble and Quartzite.

Metamorphic Rocks and their Parent Rocks The sedimentary rock Shale metamorphs into foliated Slate, Phyllite, Schist, and Gneiss. The sedimentary rock Limestone metamorphs into nonfoliated Marble. The sedimentary rock Sandstone metamorphs into nonfoliated Quartzite. The organic sedimentary rock Coal metamorphs into Anthracite.

Key Words on SOL for Metamorphic Rock Heat and Pressure!!!!! This always means metamorphic rock! Heat, pressure, hydrothermal fluids, foliated (banded), and nonfoliated (no bands)