Types of Rocks Exam PDF

IGNEOUS ROCKS CHARACTERISTICS OF IGNEOUS ROCKS  Hard: Because the minerals they contain are hard  Strong: Because the mineral crystals that make them are strong  Made of interlocking crystals that have grown into each other and lock together.  Igneous rocks are classified according...

IGNEOUS ROCKS CHARACTERISTICS OF IGNEOUS ROCKS  Hard: Because the minerals they contain are hard  Strong: Because the mineral crystals that make them are strong  Made of interlocking crystals that have grown into each other and lock together.  Igneous rocks are classified according to how they were formed and the texture and colour of the rock.  INTRUSIVE IGNEOUS ROCKS  These are formed when magma cools slowly below the Earth’s surface.  Intrusive means “forced in”. These rocks are formed between layers of other rocks as the magma is forced between them by pressure. Pegmatite is a light-colored, extremely coarse-grained intrusive  Intrusive rocks cool down igneous rock. It forms near the slowly so they form large margins of a magma chamber during crystals. the final phases of magma chamber crystallization. It often contains rare minerals that are not found in other parts of the magma chamber. The specimen shown above is about two  EXTRUSIVE ROCKS  Extrusive means “pushed out”  These rocks are formed when lava cools above ground.  The lava cools quickly so it forms rocks with very small crystals or no crystals at all. 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. The specimen shown above is about two inches (five centimeters) across.  WEATHERING Weathering is the term used to describe the physical or chemical break down of rocks. Physical Chemical Weathering: Weathering  Caused by;  Caused by:  Temperature change  The action of ice and water  Water and the chemicals in  Crystallisation of salts the water and air reacting  Wind with rock and changing it.  Living plants  EROSION AND SEDIMENTATION  Erosion is when the small particles of weathered rock are carried away by wind, water and ice.  Sedimentation describes the process by which the eroded rock particles are deposited at a particular location.  Sedimentation usually occurs where the moving water, wind or ice carrying the particles slows down.  SEDIMENTARY ROCKS  Sedimentary rocks are rocks made from sediments.  They are formed when the sediments are cemented together under pressure.  Sedimentary rocks are classified by the type of sediments they are made of.  There are three main types of sediments:  From pieces of weathered rock  From minerals crysalising in solution  From dead plant or animal material  WEATHERED ROCK SEDIMENTS  These sediments come from the weathering of all types of rocks.  They form sedimentary rocks called clastic sedimentary rocks.  Sediments form rocks when the natural cements (chemicals in water) surrounding the sediments set, holding them together.  The cements set because pressure from the weight of all the sediment layers above squeezes out the water in the bottom sediment layer causing the cementing agent to solidify.  CHEMICAL SEDIMENTS Chemical sedimentary rocks form when materials dissolved in water come out of solution, form a solid and sink to the bottom.  This process is Crystallisation, in which the dissolved minerals turn into solid crystals as the water evaporates.  Characteristics:  Contain crystals  Quite soft  Rarely have layers  Only some have fossils  ORGANIC SEDIMENTS  Organic sedimentary rocks form when dead plant matter or animal debris accumulate and is cemented together.  Characteristics:  Can be layered  Are usually soft but come can be hard.  Example: coal  USES OF SEDIMENTARY ROCKS  Due to the wide variety of sedimentary rocks they have many uses:  Examples:  Sandstone is used in buildings, walls and pavers  Limestone is used in making cement, glass and steel  Gypsum is used to make plaster  Coal is used for energy supply.  METAMORPHIC ROCKS  Metamorphic = change form  Metamorphic rocks form when high temperatures and pressure alter existing igneous and sedimentary rocks.  Changes can be physical or chemical and include the formation of new minerals not seen in the original rock.  TYPES OF METAMORPHISM  Regional metamorphism  This occurs over a wide area and is generally due to layers of rock deep underground being exposed to extreme heat and pressure.  It can also be caused by the movement of tectonic plates.  When the tectonic plates move around on top of the mantel they can collide and scrape past each other, and are heated up and compressed in the process.  Contact metamorphism  Occurs in particular local areas on a much smaller scale.  Occurs when rocks come in contact with hot magma as it pushed through the mantle and crust. TYPES EXAMPLES OF METAMORPHIC ROCKS ROCK CYCLE