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R oc ks Chapter 3 Rocks • Naturally occurring solid material made of one or more minerals • Grouped into 3 main types, based on the way it was formed IGNEOUS ROCKS • Formed from magma that cools and hardens • “Fire Formed” IGNEOUS ROCKS: 2 types • Intrusive rocks: • Extrusive rocks: – formed deep – formed from within Earth lava at Earth’s surface – Cools slowly, large crystals – Cools quickly, small crystals – Coarse grained – fine grained IGNEOUS ROCKS: texture • Size of crystal grains and chemical composition are used to classify igneous rocks – Texture depends on time it takes a rock to harden (cooling rate) IGNEOUS ROCKS: porphyry (POR-fuh-ree) • Igneous rock with a mixture of large and small crystals Two types of magma • Felsic: – Lightcolored – Thick and slow flowing – Rich in silica • Mafic: – Dark-colored – Very fluid – Rich in iron Scoria Igneous Rock Structures • Intrusions – • Extrusions – underground surface rock masses rock masses INTRUSIONS •Batholiths – largest igneous intrusions – Form when huge bodies of magma cool underground – Cover 1000 km Batholith INTRUSIONS •Laccoliths – Domelike masses formed from magma bulging upward This laccolith in Red and White Mountain, Colorado, is of Tertiary age. Overlying layers of rock have been eroded. INTRUSIONS •Dike – Sheets of igneous rocks that cut across the rock layer Dike Dike INTRUSIONS •Sill – Sheet of hardened magma that forms between and parallel to layers of rock Sill EXTRUSIONS •Volcanic neck: – The plug of hardened magma left in the vent from which lava flowed Volcanic neck: INTRUSIONS •Stock – Similar to batholiths but less than 100 km Sedimentary Rocks •75% of Earth’s surface is sedimentary rock! How Sedimentary Rocks are made: 1. Mud, sand, gravel and shells are sediments that make up rocks 2. Sediments are moved by wind and water 3. Compaction: Pressure placed in sediment layers cause them to change to rocks 4. Cementation: sediments are joined together (cemented) by minerals dissolved in water 5. This process results in the formation of layers called strata. The major characteristics of all sedimentary rocks is that they form layers! "For your information, there's a lot more to ogres than people think... Ogres are like sedimentary rocks! …Sedimentary rocks have layers... Ogres have layers! ...We both have layers." Sedimentary rocks usually form in water • Ripple marks and mud cracks Fossils often preserved in sedimentary rocks Sedimentary Rocks: Classified by • Composition • Texture • Grain size Types: 1.Clastic 2.Organic 3.Chemical 1. Clastic Rocks • Formed by broken pieces or fragments of rock • Classified according to size and shape of fragments Clastic Rocks Conglomerates: • Made of rounded pebbles and other rocks of different sizes and cemented together by clay, mud ,or sand • Formed when rivers deposit large pieces of rock • Pieces of rock rounded by water before deposited Conglomerate: Clastic Rocks Breccia: • Similar to conglomerates, but fragments are sharp and angular • Not carried far enough by water to round the edges Breccia: Clastic Rocks Sandstone: • Made of small, sand-sized grains • Very common • Resistant to wear and decay • Used to make buildings Sandstone: Clastic Rocks Mudrock: • Formed from small particles of clay • Example: shale shale shale 2. Organic Rock •Formed directly or indirectly from material that used to be living Organic Rock Fossilized Limestone: • Shells from dead animals (containing calcium carbonate) that sink to bottom of ocean floor Limestone: Organic Rock Chalk: • Composed of animals and calcium carbonate that have been pressed together Chalk Organic Rock Coal: • Rock formed from plants that lived millions of years ago 3. Chemical Rock • Formed by chemical means that do not involve any living organisms • Can occur through evaporation or chemical action Chemical Rock Limestone: • Formed directly from ocean water instead of organisms Chemical Limestone: Chemical Rock Rock salt: • Natural form of common table salt • Ex: Halite Chemical Rock Rock gypsum: Metamorphic Rocks Metamorphism: • Changing of one type of rock in to another due to 1. Tremendous heat 2. Great pressure 3. Chemical reactions ( a change in composition of minerals) Metamorphic Rocks Types of Metamorphism: 1. Contact Metamorphism • • Occurs when rocks are heated by contact with magma or lava Covers a small area 2. Regional Metamorphism • • Occurs when rocks are buried deep beneath Earth’s surface and changed by increase in temperature and pressure Covers a large area Types of Metamorphic Rock: 1. Foliated Texture: Mineral crystals arranged in parallel layers or bands (flatten under pressure) Slate Schist Gneiss (from clay or shale) (from granite, basalt, or slate) (from granite) Foliated Texture: slate Foliated Texture: phyllite: Foliated Texture: gneiss: Types of Metamorphic Rock: 2. Unfoliated Texture: • No bands of crystals • Don’t break in layers Unfoliated Texture: marble Unfoliated Texture: quartzite