Types of Rocks PDF

 Earth is a solid rock to a depth of 2,900 kilometers, where mantle meets the liquid outer core.  A rock is a naturally occurring solid aggregate of one or more minerals.  The aggregate minerals forming the rocks are held together by chemical bonds.  Grains can be different in color, t...

 Earth is a solid rock to a depth of 2,900 kilometers, where mantle meets the liquid outer core.  A rock is a naturally occurring solid aggregate of one or more minerals.  The aggregate minerals forming the rocks are held together by chemical bonds.  Grains can be different in color, texture, and sizes.  Petrology is the scientific study of rocks. Petrologists classify rocks based on how they were formed.  A rock is a naturally occurring solid mixture of one or more minerals, or organic matter  Rocks are classified by how they are formed, their composition, and texture  Rocks change over time through the rock cycle  Igneous rock begins as magma.  Magma can form: ▪ When rock is heated ▪ When pressure is released ▪ When rock changes composition  Magma freezes between 700 °C and 1,250 °C  Magma is a mixture of many minerals http://www.fi.edu/fellows/payton/rocks/create/igneous.htm  formed from hardening and crystallization of magma or molten material that originates deep within the earth.  Intrusive Igneous Rocks: magma pushes into surrounding rock below the Earth’s surface. The intrusive igneous rocks have very large crystals (coarse grained).  Extrusive Rocks: forms when magma erupts onto the Earth’s surface (lava), cools quickly with very small or no crystals formed. The crystals are very small (fine- grained) since the cooling process is fast. http://www.windows.ucar.edu/tour/link=/earth/geology/ig_intrusive.html&edu=high&fr=t  Coarse-Grained Fine-Grained Felsic Granite Rhyolite Mafic Gabbro Basalt 1. Composition - it refers to rock’s mineral and chemical make- up. Felsic – igneous rocks that are light in colors; feldspar and silicates Mafic – dark-colored igneous rocks made up of magnesium, calcium and iron Intermediate – refers to igneous rocks between mafic and felsic composition. Ultramafic – denotes igneous rocks that composed chiefly of mafic minerals. Pink rhyolite Diorite is an intermediate igneous rock with nearly equal dark and light- colored minerals. Basalt 2. Texture - overall appearance of a rock based on the size, shape, and arrangement of interlocking mineral crystals.  Aphanitic – fine-grained rocks with crystals seen by aid of microscope.  Phaneritic - coarse-grained rocks  Porphyritic – large crystals with small crystals  Glassy - a rock that looks like colored glass with no visible mineral crystal.  Pyroclastic - results from explosive fragmentation of volcanic material. A hand specimen of granite with phaneritic (coarse grained) texture. Principal minerals are Potassium Feldspar, Biotite Mica, and Quartz. A hand specimen of basalt with aphanitic (fine grained) texture. The dark color is due to abundant dark colored minerals (pyroxene, hornblende) Obsidian Ryolite Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form. Is this rock Felsic or Mafic? mafic Is it fine-grained or fine grained coarse-grained? Is this rock Intrusive or Extrusive? extrusive ▪ Meaning to change shape ▪ Changes with temperature and pressure, but remains solid ▪ Usually takes place deep in the Earth http://www.fi.edu/fellows/payton/rocks/create/metamorph.htm ▪ forms from pre-existing rocks: either metamorphic, igneous, sedimentary or other metamorphic rocks that have been altered by agents of metamorphism. ▪Examples: quartzite, marble, slate, phyllite  Metamorphism - transformation of one rock type into another.  2 types of metamorphism ✓Contact ✓Regional  Contact Metamorphism – heated by nearby magma  Increased temperature changes the composition of the rock, minerals are changed into new minerals Hornfels is a fine-grained non-foliated metamorphic rock produced by contact metamorphism http://www.windows.ucar.edu/tour/link=/earth/geology/meta_contact.html&edu=h igh&fr=t ▪ Regional Metamorphism – pressure builds up in rocks that is deep within the Earth ▪ Large pieces of the Earth’s crust collides, and the rock is deformed and chemically changed by heat and pressure http://www.windows.ucar.edu/tour/link=/earth/geology/meta_regional.html&edu=high&fr=t  1. Texture - refers to the size arrangement and grains within the rock. ✓Foliation - any planar arrangement of mineral grains or structural features within the rock.  Foliated - contain aligned grains of flat minerals Gneiss is foliated metamorphic rock that has a banded appearance and is made up of granular mineral grains. It typically contains abundant quartz or feldspar minerals.  Non-Foliated – mineral grains are not arranged in plains or bands Marble is a non-foliated metamorphic rock that is produced from the metamorphism of limestone. It is composed primarily of calcium carbonate.  Determine if the following rock samples are foliated or non-foliated: phyllite Amphibolite Quartzite Phyllite Non-foliated Non-foliated Foliated  Sedimentary rock is formed by erosion  Sediments are moved from one place to another  Sediments are deposited in layers, with the older ones on the bottom ▪ The layers become compacted http://www.fi.edu/fellows/payton/rocks/create/sediment.htm and cemented together ▪ Sedimentary Rocks are formed at or near the Earth’s surface ▪ No heat and pressure involved ▪ Strata – layers of rock ▪ Stratification – the process in which sedimentary rocks are arranged in layers Clastic – made of fragments of rock cemented together with calcite or quartz Breccia is a term most often used for clastic sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments can be filled with a matrix of smaller particles or a mineral cement that binds the rock together. Chemical sedimentary – minerals crystallize out of solution to become rock Limestone is a sedimentary rock composed primarily of calcium carbonate (CaCO3) in the form of the mineral calcite. It most commonly forms in clear, warm, shallow marine waters. It is usually an organic sedimentary rock that forms from the accumulation of shell, coral, algal and fecal debris. Organic sedimentary – remains of plants and animals Coal is an organic sedimentary rock that forms from the accumulation and preservation of plant materials, usually in a swamp environment. Coal is a combustible rock and along with oil and natural gas it is one of the three most important fossil fuels.