What is a Rock? • The material that makes up the solid parts of Earth is known as rock. • Three major types: • Igneous • Sedimentary • Metamorphic
Properties of Rocks • Physical and chemical properties of rock is determined by how and where it’s formed. • The rate at which rock weathers and the way that rock breaks apart are determined by bond strength and composition. • stability
The Rock Cycle • Any of the three major types of rock can be changed into another of the three types. • Rock cycle the processes in which rock forms, changes, is destroyed, and forms again by geological processes
Stages of the Rock Cycle • Magma forms when rocks melt. • Igneous rock forms when magma, or molten rock, cools and hardens. • Sedimentary rock forms when deposited sediment is compressed and cemented together • Sediments are rocks and other matter that has been broken into fragments by weathering and erosion. • Metamorphic rock forms when existing rock is altered by heat and pressure.
Bowen’s Reaction Series • Illustrates the order in which minerals crystallize from cooling magma according to their chemical composition and melting point
Rock melts when… • the temperature increases to above its melting point • excess pressure is removed from rock that is hotter than its melting point. • fluids are added. Presence of fluids generally decreases the melting point.
Partial Melting • Different minerals have different melting points • Lower melting points melt first • As minerals melt, the magma’s composition changes.
Fractional Crystallization • The crystallization and removal of different minerals from the cooling magma is called • When magma cools, the cooling process is the reverse of the process of partial melting.
Types of Igneous Rock • Intrusive forms from the cooling and solidification of magma beneath Earth’s surface • Extrusive forms from the cooling and solidification of lava at Earth’s surface • The texture of igneous rock is determined by the size of the crystals in the rock, which is determined by the cooling rate of the magma.
Igneous Textures Coarse-Grained • Because intrusive igneous rocks cool slowly, they commonly have large mineral crystals. Fine-Grained • Because extrusive igneous rocks cool rapidly, they are commonly composed of small mineral grains.
Other Igneous Rock Textures • Porphyritic texture- large crystals within a matrix of smaller crystals. • Phaneritic- crystals all same size • Aphanetic- crystals too small to see • Glassy Texture- no crystals • Vesicular texture- dissolved gases are trapped as bubbles in the rock.
Igneous Composition • Determined by the chemical composition of the magma from which came. Felsic Rock • Rich in feldspars and silica and is light in color
Igneous Composition Mafic Rock • Rich in magnesium and iron and dark in color Intermediate Rocks • contain lower amount of silica than felsic but higher amounts of silica than mafic.
Extrusions • Igneous rock masses that form on Earth’s surface. • Volcanoes, lava flows, and tuff layers are other common extrusions.
Sedimentary Rock • Made of combinations of different types of sediment, such as fragments of rock, minerals, and organic materials.
Lithification • Process of loose sediment is converted into sedimentary rock by compaction and cementation. • compaction the process in which sediment is pressed together by the weight of overlying layers • cementation the process in which minerals bind sediments together to form rock
Types of Sedimentary Rock • There are three main classes of sedimentary rocks—chemical, organic, and clastic. • Classification is based on the shape, size, and composition of the sediments that form the rocks.
chemical sedimentary rock • Forms when minerals precipitate from a solution or settle from a suspension • Rocks that form through evaporation are called evaporites. • Gypsum and halite (table salt) are common evaporites.
organic sedimentary rock • Forms from the remains of plants or animals • Coal • Organic limestones • Dead shells accumulate and are compacted to form limestone.
clastic sedimentary rock • Forms when fragments of preexisting rocks are compacted or cemented together • Clastic sedimentary rocks are classified by the size of the sediments they contain.
Types of clastic sedimentary rock • Conglomerate- contains large, rounded pieces. • Breccia- contains large, angular pieces. • Sandstone- composed of sand-sized grains. • Shale- composed of clay-sized particles.
Physical Characteristics of Sediments • Sediments are transported by four main agents: water, ice, wind, and the effects of gravity. • The distance it is moved and the agent that moves it determine the characteristics of that sediment.
Sorting • The tendency for sediments to separate according to size. • Well-sorted = same size and shape. • Poorly sorted = many different sizes. • Faster-moving currents can carry larger particles than slower-moving currents can.
Angularity • As sediment is transported it collides with other objects. • Causes the particles to change size and shape. • When particles first break from the source rock they tend to be angular and uneven. • In general, the farther sediment travels from its source, the finer and smoother the particles become.
Stratification • Layering of sedimentary rock which occurs when the conditions of sediment deposition change. • Stratified layers are called beds. • Depositional environment- setting in which sediment is deposited
Sedimentary Features Cross-Beds and Graded Bedding • Cross-beds, or slanting layers of rock, form in sand dunes or river beds. • Graded bedding is a feature in sediments are deposited with the larger grains at the bottom and finest grains at the top.
Sedimentary Features Ripple Marks • Ripple marks form when air or water flows over sand and the ripples are preserved in the rock. • Commonly at the beach or on a river bed.
Sedimentary Features Cont’d Mud Cracks • Mud cracks form when muddy deposits dry and shrink. The shrinking causes the drying mud to crack. • Mud cracks form on river floodplains or on dry lake beds.
Sedimentary Features Cont’d Fossils and Concretions • Fossils are the remains of organisms that are preserved in rock. • Concretions are lumps of minerals that precipitate from fluids and build up around a nucleus or in a cavity in existing rock.
Metamorphism • Process in which one type of rock changes into metamorphic rock • During metamorphism, heat, pressure, and hot fluids cause some minerals within the rock to change.
Factors Affecting Metamorphism • The type of rock that forms indicates the conditions under which the original rock changed. • Factors Affecting Metamorphism • Composition of the parent rock • The amount and direction of pressure • The presence or absence of fluids
Types of Metamorphism Contact Metamorphism • Change in the texture, structure, or chemistry of rock due to contact with magma Hydrothermal Metamorphism • Very hot water reacts with rock
Types of Metamorphism Regional Metamorphism • Change in the texture, structure, or chemistry of rock due to occurring over a large area, generally are a result of tectonic forces
Metamorphic Textures Foliated Rocks • Minerals grains are arranged in planes or bands • Extreme pressure may cause the mineral crystals in the rock to realign into alternating light and dark parallel bands. • Foliated metamorphic rocks include the common rocks slate, schist, and gneiss.
Metamorphic Textures Nonfoliated Rocks • Minerals grains are not arranged in planes or bands • Some tend to be less diverse in chemical compositions than foliated metamorphic rocks. • Others contain grains that have more stable structure and do not change shape as readily as a result of temperature and pressure changes • Ex: marble and quartzite.