SCIENCE STARTER – LABEL THE PARTS OF THE EARTH AND THEN SIT QUIETLY AND WAIT FOR FURTHER INSTRUCTIONS.

Chapter 3, Section 3.1 “Rock Recycling” IGNEOUS ROCKS AND SEDIMENTARY ROCKS

 Rock Cycle  Power Sources for Rock Cycle LOOKING BACK

 What is the driving force for the rock cycle’s igneous rock and metamorphic rock formation?  The heat from the interior of the Earth.  What happens when sediments reach a basin?  They are cemented and compacted into sedimentary rock.  What happens when a rock is exposed to heat/pressure?  It can change into a metamorphic rock. LET’S REVIEW

 Tomorrow we start our 2-day lab of mineral identification and properties. TEST THURSDAY, PLEASE STUDY LOOKING AHEAD

IGNEOUS ROCKS

 How does igneous rock form?  From magma or lava as it cools and hardens.  Different kinds of igneous rocks form when magma and lava cool and harden.  Depends on where and how quickly! INTRODUCTION

 Igneous comes from the Latin word ignis which means “fire”.  Igneous rocks are often associated with fiery volcanic eruptions  But they also form deep within the Earth’s surface. FORMATION OF IGNEOUS ROCKS

 Rocks that form when magma hardens beneath Earth’s surface are called intrusive igneous rocks.  They ‘intrude’ on existing rocks!  We would never see these rocks if not for EROSION!  Stone Mountain, GA  Magma consists mainly of the elements silicon and oxygen  Aluminum, Iron, Calcium, Sodium, Potassium, and magnesium.  Also has gases like water vapor!  These gases are kept within the magma by the pressure of surrounding rocks.  This makes magma less dense  Magma works it’s way to the surface! TYPES OF IGNEOUS ROCKS - INTRUSIVE

 As the magma rises, it cools, allowing elements to combine and form minerals!  Minerals grow in size until they form a mass of interlocking crystals.  Granite is a common intrusive igneous rock—you can see the interlocking mineral crystals! INTRUSIVE IGNEOUS ROCKS

 What is magma called on the Earth’s surface?  Lava is similar to magma, except that the gases in lava have ESCAPED  No longer rock holding them in place.  Lava hardens, and the rocks that form from lava are called extrusive igneous rocks.  They are ‘extruded’ onto the surface.  Crystals did not have as long to form, so they are smaller and you cannot pick out mineral crystals. EXTRUSIVE IGNEOUS ROCKS

 Texture and Composition are two characteristics used to classify igneous rocks.  As you can see, igneous rocks can look very different so it is important to have a way to classify them!  Texture describes the appearance of an igneous rock based on its size, shape, and arrangement of its interlocked crystals.  Composition classes of igneous rocks are based on the proportions of light and dark minerals in the rock. CLASSIFICATION OF IGNEOUS ROCKS

TEXTURE OF IGNEOUS ROCKS

 Rate of cooling really affects the texture of igneous rock.  If magma cools slowly, a few centers of crystal growth develop.  Allows charged atoms to move large distances in the magma.  Slow cooling results in large crystal size.  Igneous rocks with course- grained texture have large crystals. COURSE-GRAINED TEXTURE

 If cooling of magma or lava happens quickly, the ions in the melted material lose their motion and quickly combine.  Large number of tiny crystals that all compete for available ions.  Results in small, interconnected mineral grains.  Igneous rocks with fine- grained texture have small crystals. FINE-GRAINED TEXTURE

 When lava spews onto the Earth’s surface, there may not be enough time for the ions in lava to arrange themselves into a network of crystals.  Solids made this way are composed of randomly assorted ions.  Rocks are said to have a “glassy” texture  Pumice and Obsidian GLASSY TEXTURE

 A large body of magma deep in the earth takes tens of thousands of years to harden.  Minerals in this magma do not crystallize at the same rate or at the same time.  Some crystals get quite large before others even start forming.  Rocks like this have large crystals surrounded by smaller ones.  Rocks with very different size minerals experience different rates of cooling.  These rocks are said to have porphyritic texture. PORPHYRITIC TEXTURE

COMPOSITION OF IGNEOUS ROCKS

 One group of igneous rocks includes those that are made almost entirely of the light- colored silicate minerals quartz and feldspar.  Rocks with these main ingredients are said to have a granitic composition!  Also contain 10% dark silicate minerals like biotite mica and amphibole.  Granitic rocks are 70% silica and are major rocks in the continental crust. GRANITIC COMPOSITION

 Rocks that contain many dark silicate minerals and plagioclase feldspar have a basaltic composition.  Rich in magnesium and iron.  Darker and denser than most granitic rocks because of their iron content.  Most common basaltic rock is basalt.  Gabbro is also common. BASALTIC COMPOSITION

ANDESITIC  Rocks with a composition between granitic and basaltic have an andesitic composition.  Named after volcanic rock andesite.  Andesitic rocks are 25% dark silicate minerals  Amphibole, pyroxene, biotite mica  75% plagioclase feldspar. PERIDOTITE  Contains mostly the minerals olivine and pyroxene.  Composed almost entirely of dark silicate minerals so its chemical composition is called ultramafic.  Rare at Earth’s surface  Much of upper mantle is peridotite (so we think) OTHER COMPOSITIONAL GROUPS

 Igneous rocks form when magma or lava cools and hardens.  Intrusive rocks: form beneath the surface.  Extrusive rocks: form on/at the surface.  Igneous rocks can be classified by TEXTURE or by COMPOSITION. SUMMARY

SEDIMENTARY ROCKS

 All sedimentary rocks begin to form when existing rocks are broken down into sediments.  Sediments (consist mainly of weathered rock debris) are often transported to other places.  Sediments are dropped and eventually become compacted and cemented to form sedimentary rocks. INTRODUCTION

 Sedimentary comes from the Latin word sedimentum which means “settling”.  Sedimentary rocks form when solids settle out of a fluid such as water or air. FORMATION OF SEDIMENTARY ROCKS

 Recall that weathering is any process that breaks rocks into sediments (we will go into more detail in a later chapter).  Weathering is often the FIRST STEP to sedimentary rock formation!  Chemical Weathering takes place when the minerals in the rocks change into other substances.  Weathering also happens when physical forces break rocks into smaller pieces!  Living things can cause physical weathering as well! WEATHERING, EROSION, AND DEPOSITION

 Weathered sediments do not usually stay in place.  Water, wind, ice, or gravity carries sediments to a new place.  Erosion involves weathering and the removal of rock.  When an agent of erosion (water, wind, ice, or gravity) loses energy, it drops the sediments. This process is called deposition. WEATHERING, EROSION, AND DEPOSITION

 Sediments are deposited according to size.  Largest sediments (like pebbles in conglomerates) are deposited first, and then smaller sediments are deposited later.  Some sediments are so small they get carried long distances before being deposited! WEATHERING, EROSION, AND DEPOSITION

 After sediments are deposited, they often become lithified.  Turned into stone.  Compaction and cementation change sediments into sedimentary rock.  Compaction is a process that squeezes, or compacts, sediments.  Caused by the weight of sediments.  Water is driven out of sediments. COMPACTION AND CEMENTATION

DRIVING WATER OUT – FLAME STRUCTURES

 Cementation takes place when dissolved minerals are deposited in the tiny spaces among the sediments.  Cement can be seen with the naked eye (conglomerate) or it can be microscopic (sandstone). COMPACTION AND CEMENTATION

CLASSIFICATION

 Sedimentary rocks can be classified into two main groups according to the way they form.  First group is rocks that are made of weathered bits of rocks and minerals.  Clastic Sedimentary Rocks  Second group forms when dissolved minerals precipitate from water solutions.  Chemical Sedimentary Rocks CLASSIFICATION OF SEDIMENTARY ROCKS

 Many different minerals found in clastic rocks.  Most common: clay minerals, a product of weathering.  Grouped according to size of minerals.  Rounded, gravel-size or larger particles: conglomerate  Particles are angular: breccia  Sandstone: rock where the sediments are grain-sized.  Shale is the most common sedimentary rock and it is made of very fine-grained sediment.  Siltstone CLASTIC SEDIMENTARY ROCKS

 Form when dissolved substances precipitate, or separate, from water solutions.  Generally occurs when water evaporates or boils off, leaving solid product behind.  Examples: limestone, rock salt, chert, flint, gypsum  90% of limestones are formed from biochemical sediments.  Shells and skeletal remains of organisms that settle to the ocean floor.  Coquina and Chalk CHEMICAL AND BIOCHEMICAL SEDIMENTARY ROCKS

 Sedimentary rocks are used to unravel the Earth’s past.  The many unique features of sedimentary rocks are clues to how, when, and where the rocks formed.  Each layer of a sedimentary rock records a period of sediment deposition.  Oldest layer of sediment is found at the bottom.  Youngest layer of sediment is found at the top. FEATURES OF SEDIMENTARY ROCKS

 Ripple marks may indicate the rock formed in a river, lake, or ocean.  Mud cracks mean wet mud or clay dried and shrank— meaning the rock formed in a dry environment. FEATURES OF SEDIMENTARY ROCKS

 Fossils are traces of ancient life, and are unique to some sedimentary rocks.  If we know what kind of environment the fossil used to live in, then we know what conditions the rock formed in!  Fossils can help match up rock units in different places that are the same age. FEATURES OF SEDIMENTARY ROCKS

 Sedimentary rocks form from four major processes:  WEATHERING produces particles called sediments  Wind, water, ice, and gravity DEPOSIT these sediments  Sediments are COMPACTED and CEMENTED to form rocks  Classified according to how they form and what they are made of. SUMMARY