Rocks Sedimentary, Igneous, and Metamorphic
3 Types of Sedimentary Rocks • Clastic • Chemical • Organic
Clastic Sedimentary Rock • Sediments form when rocks are weathered and eroded • Sediments are moved by wind, glaciers and water • Most clastic sediments are deposited in the ocean
Clastic Sedimentary Rock • Sediments are converted into solid sedimentary rock by the processes of compaction and cementation.
Clastic Sedimentary Rock Compaction & Cementation
Clastic Sedimentary Rock Compaction & Cementation
Clastic Sedimentary Rock • Compaction occurs when the weight of overlying materials compresses the deeper sediments. • Cementation occurs when soluble cementing materials, such as calcite, silica, and iron oxide, are precipitated onto sediment grains, fill open spaces, and join the particles.
Clastic Sedimentary Rock • Particle (clast) size is key to type of rock • Gravel is > 2 mm • Sand is 1/16 mm to 2 mm • Mud is < 1/16 mm • Clay is < 4 um • Silt is > 4 um
Chemical Sedimentary Rock • Chemical sedimentary rocks are made of mineral crystals that formed from chemicals dissolved in water. • The water in the oceans, lakes, and underground is often full of dissolved minerals and other elements.
Chemical Sedimentary Rock • When water is so full of elements that not all will fit, some are not able to remain dissolved. • They come out of solution, or precipitate, forming solid mineral crystals. • Precipitation is the opposite of dissolving.
Chemical Sedimentary Rock • Minerals precipitate when some water has been evaporated or when a chemical reaction occurs. • Evaporation takes only water molecules into the atmosphere so the elements in the remaining liquid water become very concentrated. Eventually, they do not all fit and some precipitate out as mineral.
Organic Sedimentary Rock Coal • Coal: Bituminous & Anthracite Anthracite Bituminous
Organic Sedimentary Rock Coal • Coal is an organic sedimentary rock that has been altered slightly by being compressed and heated. • It was formed by the rapid burial of large numbers of plants; swamp forest. • Over time the plant material is compacted so much by the weight of the overlying sediment that it is turned in to rock.
Igneous Rocks • Magma is the molten rock material below the surface. • Lower density causes magma to rise toward the surface (compared to the surrounding rock). • Magma at the surface is lava. • Igneous rocks are formed from solidified/cooled magma or lava. • Igneous rocks are made of interlocking crystals
Igneous Rocks Magma extruded onto the Earth’s surface forms volcanic or extrusive igneous rocks. Magma that crystallizes within the Earth’s crust forms plutonic or intrusive igneous rock.
Extrusive & Intrusive Igneous Rocks • Intrusive- Magma under the surface • Coarse-grained (igneous rock) • Magma cools slowly and large crystals grow over a long period of time • Gabbro, diorite, granite
Extrusive & Intrusive Igneous Rocks • Extrusive- Lava at the surface • Fine-grained (igneous rock) • Lava cools very quickly, consequently crystals do not have time to grow and develop • Basalt, andesite, rhyolite, obsidian
Igneous Rocks Molten rock or magma(1,000-1,200 oC), contains chemical elements. If the magma begins to cool, elements begin to form chemical bonds within the magma and crystals start to develop.
Igneous Rocks Rocks that form from magma or lava cooled from high temperatures tend to contain a lot of iron and magnesium but little silica. These rocks are called mafic and tend to be dominated by dark colored minerals such as amphibole and pyroxene (Elements: iron & magnesium).
Igneous Rocks When magma cools slowly, minerals that form at cooler temperatures dominate the resulting rock. These rocks are called felsic and tend to be light colored with minerals such as feldspar and quartz. (Elements: silicon, oxygen, sodium, potassium, & aluminum)
Igneous Rocks Classification of Igneous Rocks -Texture: crystal size -Color -Mineral composition
Igneous Rocks • Granite • Felsic • Intrusive
Igneous Rocks • Rhyolite • Felsic • Extrusive
Igneous Rocks • Basalt • Mafic • Extrusive
Igneous Rocks • Gabbro • Mafic • Intrusive
Igneous Rocks • Andesite • Intermediate • Extrusive
Igneous Rocks • Diorite • Intermediate • Intrusive
Igneous Rocks • Other Igneous Rocks • Lava flows • Fragmented magma ejected explosively • Ash plumes • Pyroclastic flows • Cool and solidify very quickly; no minerals develop • Consequently they cannot be mafic, intermediate, or felsic
Igneous Rocks • Obsidian • Extrusive
Igneous Rocks • Pumice • Extrusive
Metamorphic Rocks The Greek word meta means “change” and morph meaning “shape”. Metamorphic rocks were previously either sedimentary or igneous rocks, but they have been subjected to very high temperature and pressure. (Below the surface of the Earth)
Metamorphic Rocks The temperature was not high enough to make the rock melt (Metamorphic changes occur as the rock is in solid-state), but it was high enough to allow some crystals to grow, and for the minerals to begin to re-crystallize and thus form a new rock. As temperature rises, crystal lattices are broken down and reformed with different combinations of atoms. New minerals are formed.
Metamorphic Rocks • The types of metamorphism • Regional metamorphism • Contact metamorphism Regional metamorphism Contact metamorphism
Metamorphic Rocks Contact metamorphism In the case of contact metamorphism heat comes from contact with molten magma. -This type of metamorphism has a limited and local effect.
Metamorphic Rocks Regional metamorphism When rocks are forced toward the mantle during the formation of a mountain range and/or other tectonic activity, regional metamorphism occurs. -Large volumes of rock are altered in this way.
Metamorphic Rocks Metamorphism does not take place on the Earth’s surface. Rocks under the Earth’s surface are under great pressure from overlying rock layers. Deep burial- as depth increases, in the Earth’s crust, the temperature also increases. Tectonic forces in the Earth may apply lateral pressure to large volumes of rock.