Rocks Lesson 1:

Rocks Lesson 1: Rocks and the Rock Cycle

by Mrs. Hockersmith

Rocks

Rocks are everywhere. Mountains, valleys, and the seafloor are made of rocks. Parts of your home are likely made of rock. Floors, countertops, and some tabletops are made of rock. A rock is a natural, solid mixture of minerals or grains. These particles are made of mineral crystals, broken minerals, or rock fragments. Sometimes a rock can also include remains of an organism or volcanic glass. Processes on Earth’s surface can cause rocks to break apart into fragments. Geologists call the fragments that make up a rock grains. Grains are identified according to the grain’s shape, size, and chemical composition. Overall, rocks are classified according to their texture and composition.

Multiple Choice

Grains are identified according to their

• size

• shape

• Chemical composition

• all of the above

Multiple Choice

Which one of these are particles in rocks NOT made of

• mineral crystals

• Broken Minerals

• synthetic diamonds

• rock fragements

​Two observations Scientists use #1

​A rock’s texture is one way that geologists classify rocks. The grain size and the way grains fit together in a rock are called texture. When a geologist classifies a rock by its texture, he or she looks at the size of minerals or grains in the rock, the arrangement of the individual grains, and the overall feel of the rock. Texture helps geologists determine the environment in which a rock formed. For example, a rock that has many smooth grains was likely formed by strong forces acting on the rock.

Multiple Choice

texture helps geologists determine the _______ in which a rock formed

• environment

• laboratory

• volcano

• planet

​Two observations scientists use #2

​The second thing scientists use to classify a rock is its composition. This is the type of grains that makeup a rock. Rocks that formed inside a volcano have a different composition from rocks that formed along a river. Geologists use maps, field journals, compasses, rock hammers, and other tools to help classify a rock’s texture and composition. These tools also help geologists interpret how a rock formed. When geologists identify certain minerals, they can conclude that a rock formed under extreme temperature and pressure. The presence of other minerals suggests to geologists that a rock formed from molten material deep below Earth’s surface.

Multiple Choice

A rocks composition can help scientists

• decide where the rock was made in a lab

• decide where the rock formed in nature

• get rich

• find other rocks

​Three major rock groups

​Rocks are classified, or placed into groups, based on how they form. The three major groups are igneous rocks, sedimentary rocks, and metamorphic rocks. Each rock type can be described by both physical and chemical characteristics. Geologists interpret the environment in which the rocks formed based on these characteristics.

​Igneous Rocks

Igneous rocks form from magma. Magma is molten, or liquid, rock underground. As the magma, or molten rock cools, mineral crystals form. These crystals become the grains in an igneous rock. Magma can cool on Earth’s surface or deep within Earth. Molten rock that erupts on Earth’s surface is called lava. Igneous rock forms when the magma or lava cools and crystallizes. Igneous rock forms in many environments, such as subduction zones, mid-ocean ridges, and around hot spots where volcanoes are common.

Multiple Choice

Molten rock that erupts ON earths surface is called

• magma

• lava

• ro

• crystals

Multiple Choice

Igneous rocks often form near ________, mid ocean ridges, and hot spots

• villages

• subduction zones

• fields

• in caves

​Sedimentary Rocks

​Rocks on Earth’s surface can break down and be transported to new environments by 4 main forces. Wind, running water, ice, and gravity break down rocks on Earth’s surface.

​

Sediment is rock material that forms where rocks are broken down into smaller pieces or dissolved in water as rocks erode. These materials are the building blocks of sedimentary rocks and include rock fragments, mineral crystals, and the remains of certain plants and animals. Sedimentary rocks form where sediment is deposited. Environments in which sedimentary rocks are formed include rivers, streams, mountain valleys, and deserts.

Multiple Choice

Wind, _____, ice, and gravity break down rocks

• tornadoes

• still water

• sleet

• running water

​Metamorphic Rocks

​Metamorphic rocks form when preexisting rocks are exposed to extreme temperatures, extreme pressure, or chemical fluids. This causes changes to both the composition and texture of the rock.

​

In many cases, the grains of the rock appear as bent or twisted layers. Metamorphic rocks can form from any igneous or sedimentary rock. Even other metamorphic rocks can be formed into new metamorphic rocks by extreme conditions. For example, granite is an igneous rock. It can metamorphose, or change, into gneiss. The sedimentary rock limestone can metamorphose into marble. Metamorphic rock often forms along plate boundaries, where extreme temperatures and intense pressure occur.

Multiple Choice

Which example of igneous rock did I just give

• gneiss

• topaz

• granite

• magma

​The Rock Cycle

​Rocks are changing all the time, although you can’t usually observe these changes. The series of processes that change one type of rock into another type of rock is called the rock cycle. Forces on Earth’s surface and deep within Earth drive the rock cycle. The cycle describes how natural processes work to change one rock type into another rock type. One example is igneous rock that begins as lava. The lava cools and crystallizes. Over time, water erodes this rock to form sediments that eventually cement together to become sedimentary rock. Some of the other processes rocks go through include melting, cooling and crystallization, heat and pressure, compaction and cementation, and erosion and deposition. There is no true beginning or end to the rock cycle.

Multiple Choice

Which is the beginning of the rock cycle?

• se

• Igneous

• metamorphic

• There is none