THE STUDY OF ROCKS

By Tahanee Hasan

Heather Kribs

Debra Kern-Shuman

Introduction

In this lesson, you will learn about the three main types of rock, find out how to tell the different rock types apart, and see how rocks change from one type into another!

ROCKS come in cool colors, shapes, textures, and sizes and are found all around you, but how much do you REALLY know about them?

Types of Rocks

Rocks are not all the same!

The three main types, or classes, of rock are sedimentary, metamorphic, and igneous and the differences among them have to do with how they are formed.

SedimentarySedimentary rocks are formed from particles of sand, shells, pebbles, and other fragments of material. Together, all these particles are called sediment. Gradually, the sediment accumulates in layers and over a long period of time hardens into rock. Generally, sedimentary rock is fairly soft and may break apart or crumble easily. You can often see sand, pebbles, or stones in the rock, and it is usually the only type that contains fossils.

Examples of this rock type include conglomerate and limestone.

MetamorphicMetamorphic rocks are formed under the surface of the earth from the metamorphosis (change) that occurs due to intense heat and pressure (squeezing). The rocks that result from these processes often have ribbonlike layers and may have shiny crystals, formed by minerals growing slowly over time, on their surface.

Examples of this rock type include gneiss and marble.

Types of RocksIgneous

IgneousIgneous rocks are formed when magma (molten rock deep within the earth) cools and hardens. Sometimes the magma cools inside the earth, and other times it erupts onto the surface from volcanoes (in this case, it is called lava). When lava cools very quickly, no crystals form and the rock looks shiny and glasslike. Sometimes gas bubbles are trapped in the rock during the cooling process, leaving tiny holes and spaces in the rock.

http://www.blinkx.com/watch-video/dr.-loopy-discusses-igneous-rocks/v5vi98GdQI1cM5RYU-Smlg Examples of this rock type include basalt and obsidian.

Obsidian More Igneous RocksBasalt

Classifying Rocks:What To Look For

Listed below are some of the key characteristics that can help you identify the rocks within these three main classes.

CrystalsSmall, flat surfaces that are shiny or sparkly, like tiny mirrors.

FossilsImprints of leaves, shells, insects, or other items in the rock.

Gas bubbles"Holes," like Swiss cheese, in the rock.

Glassy surfaceA shiny and smooth surface, like colored glass.

Ribbonlike layersStraight or wavy stripes of different colors in the rock.

Sand or pebblesIndividual stones, pebbles, or sand grains visible in the rock.

How Rocks ChangeDoes it seem to you that rocks never change? For example, if you find a chunk of granite today, can you expect that it will still be granite at the end of your lifetime? That may well be true — but only because our lifetimes are very short relative to the history of the earth.

If we take a step back to look at geologic time (which focuses on changes taking place over millions of years), we find that rocks actually do change! All rocks, in fact, change slowly from one type to another, again and again. The changes form a cycle, called "the rock cycle."

The way rocks change depends on various processes that are always taking place on and under the earth's surface. Now let's take a closer look at each of these processes.

How Rocks ChangeHeat & Pressure

What happens to cookie dough when you put it in the oven? The heat of the oven produces changes in the ingredients that make them interact and combine. Without melting the dough, the heat changes it into a whole new product — a cookie.

A similar process happens to rocks beneath the earth's surface. Due to movements in the crust, rocks are frequently pulled under the surface of the earth, where temperatures increase dramatically the farther they descend. Between 100 and 200 kilometers (62 and 124 miles) below the earth's surface, temperatures are hot enough to melt most rocks. However, before the melting point is reached, a rock can undergo fundamental changes while in a solid state — morphing from one type to another without melting.

An additional factor that can transform rocks is the pressure caused by tons of other rocks pressing down on it from above; heat and pressure usually work together to alter the rocks under the earth's surface. This kind of change, which results from both rising temperature and pressure, is called metamorphism, and the resulting rock is a metamorphic rock.

The Rock Cycle Diagram

A useful way to illustrate how the three main types of rock are related to one another and how changes to rocks happen in a recurring sequence is the rock cycle. It can be presented in a diagram like the one below.

The concept of the rock cycle is attributed to James Hutton (1726—1797), the 18th-century founder of modern geology. The main idea is that rocks are continually changing from one type to another and back again, as forces inside the earth bring them closer to the surface (where they are weathered, eroded, and compacted) and forces on the earth sink them back down (where they are heated, pressed, and melted). So the elements that make up rocks are never created or destroyed — instead, they are constantly being recycled. The rock cycle helps us to see that the earth is like a giant rock recycling machine!

Resources

www.geology.com

www.Shelledymesa.K12.com

www.learner.org/interactives/rockcycle/Index.html

State Goals• STATE GOAL 11: Understand the processes of scientific inquiry and technological design to investigate questions, conduct experiments and solve problems.• Why This Goal Is Important: The inquiry process prepares learners to engage in science and apply methods of technological design. This understanding will enable

students to pose questions, use models to enhance understanding, make predictions, gather and work with data, use appropriate measurement methods, analyze results, draw conclusions based on evidence, communicate their methods and results, and think about the implications of scientific research and technological problem solving.

•  • A. Know and apply the concepts, principles and processes of scien tific inquiry.• LATE ELEMENTARY• 11.A.1a Describe an observed event.• 11.A.2a Formulate questions on a specific science topic and choose the steps needed to answer the questions.• 11.A.1b Develop questions on scientific topics.• 11.A.2b Collect data for investigations using scientific process skills including observing, estimating and measuring.• 11.A.2c Construct charts and visualizations to display data.• 11.A.4c Collect, organize and analyze data accurately and precisely.• 11.A.2d Use data to produce reasonable explanations.• 11.A.1e Arrange data into logical patterns and describe the patterns.• 11.A.2e Report and display the results of individual and group investigations. • 11.A.5e Report, display and defend the results of investigations to audiences that may include professionals and technical experts.• 11.A.3f Interpret and represent results of analysis to produce findings.• 11.A.3g Report and display the process and results of a scientific investigation.•  •  •  •  

State Goals• STATE GOAL 12: Understand the fundamental concepts, principles and interconnections of the life, physical and earth/space sciences.• Why This Goal Is Important: This goal is comprised of key concepts and principles in the life, physical and earth/space sciences that have considerable explanatory

and predictive power for scientists and non-scientists alike. These ideas have been thoroughly studied and have stood the test of time. Knowing and being able to apply these concepts, principles and processes help students understand what they observe in nature and through scientific experimentation. A working knowledge of these concepts and principles allows students to relate new subject matter to material previously learned and to create deeper and more meaningful levels of understanding.

•  • E. Know and apply concepts that describe the features and processes of the Earth and its resources.• LATE ELEMENTARY• 12.E.1a Identify components and describe diverse features of the Earth’s land, water and atmospheric systems.• 12.E.2a Identify and explain natural cycles of the Earth’s land, water and atmospheric systems (e.g., rock cycle, water cycle, weather patterns).• 12.E.3a Analyze and explain large-scale dynamic forces, events and processes that affect the Earth’s land, water and atmospheric systems (e.g., jetstream, hurricanes,

plate tectonics).• 12.E.4a Explain how external and internal energy sources drive Earth processes (e.g., solar energy drives weather patterns; internal heat drives plate tectonics).• 12.E.5 Analyze the processes involved in naturally occurring short-term and long-term Earth events (e.g., floods, ice ages, temperature, sea-level fluctuations).• 12.E.3b Describe interactions between solid earth, oceans, atmosphere and organisms that have resulted in ongoing changes of Earth (e.g., erosion, El Nino).• 12.E.4b Describe how rock sequences and fossil remains are used to interpret the age and changes in the Earth.•  

AssessmentGo to www.learner.org/interactives/rockcycle/Index.html throughout presentation

Sedimentary Rocks• What Is a Sedimentary Rock?• Have you ever been to the beach and nestled your toes in the sand? Over thousands of years that sand

might become part of a sedimentary rock!• Sedimentary rocks make up about three-quarters of the rocks at the Earth’s surface. They form at the

surface in environments such as beaches, rivers, the ocean, and anywhere that sand, mud, and other types of sediment collect. Sedimentary rocks preserve a record of the environments that existed when they formed. By looking at sedimentary rocks of different ages, scientists can figure out how climate and environments have changed through Earth’s history.Fossils of ancient living things are preserved in sedimentary rocks too.

• Many sedimentary rocks are made from the broken bits of other rocks. These are called clastic sedimentary rocks. The broken bits of rocks are called sediment. Sediment is the sand you find at the beach, the mud in a lake bottom, the pebbles in a river, and even the dust on furniture. The sediment may, in time, form a rock if the little pieces become cemented together.

• There are other types of sedimentary rocks whose particles do not come from broken rock fragments. Chemical sedimentary rocks are made of mineral crystals such as halite and gypsum formed by chemical processes. The sediment particles of organic sedimentary rocks are the remains of living things such as clamshells, plankton skeletons, dinosaur bones, and plants.

Ripples in beach sand , such as those in the upper photograph (A) may someday become a rock like the sandstone in the lower photograph (B). This sandstone was part of a beach over 200 million years ago in the Triassic period.

Brecia, Chert, Coal, Conglomerate, Iron Ore, Limestone, Rocksalt, Sandstone, Shale, Siltstone