Lesson 3 Igneous Rocks

How do geologists classify igneous rocks?

● Igneous rocks are classified by their origin, texture, and mineral composition○ Origin

■ Igneous rocks may form on or beneath Earth’s surface ■ Extrusive rock is igneous rock formed from lava on Earth’s surface

● Basalt is the most common extrusive rock■ Intrusive rock is igneous rock formed from magma underground

● Granite is the most common intrusive rock

How do geologists classify igneous rocks?

● Igneous rocks are classified by their origin, texture, and mineral composition○ Texture

■ Depends on the size and shape of its mineral crystals ■ Rapidly cooling lava forms fine-grained igneous rocks with little to no

crystals ■ Slow cooling magma forms coarse-grained igneous rocks with large crystals

How do geologists classify igneous rocks?

● Igneous rocks are classified by their origin, texture, and mineral composition○ Mineral composition

■ Lava that has little silicon and oxygen form dark colored rocks like basalt● Basalt contains the minerals feldspar and other dark colored minerals

■ Magma that has a lot of silicon and oxygen form light colored rocks like granite

● Granite contains the minerals quartz, feldspar, hornblende, and mica

How are igneous rocks used?

● Igneous rocks are hard, dense, and durable● Many people use them for tools and building materials

○ Granite has been used for more than 3,500 years ■ It was first used to build statues and fortresses ■ Nowadays, it is used for bridges, buildings, flooring, cobblestones, and much

more!

○ Pumice and obsidian are other igneous rocks with building uses■ Pumice is used as an abrasive for cleaning and polishing ■ Obsidian has been used for sharp tools for cutting or scraping

Lesson 4 Sedimentary Rocks

How do sedimentary rocks form? ● Sediment is small, solid pieces of material that come from rocks or

living things ● Sedimentary rocks form when sediment is deposited by water and

wind○ Most sedimentary rocks are formed through a sequence of processes

i. Weathering & erosionii. Deposition

iii. Compactioniv. Cementation

How do sedimentary rocks form? ● Most sedimentary rocks are formed through a sequence of

processes○ Weathering & Erosion

■ Weathering is the effect of freezing and thawing, acid, plant roots, and other forces on rocks

■ After the rocks are broken up, the fragments are carried away by erosion, the process where running water, wind, or ice carry away broken-up rock

How do sedimentary rocks form? ● Most sedimentary rocks are formed through a sequence of

processes○ Deposition

■ Deposition is the process where sediment settles out of the water or wind carrying it and is deposited in layers on the ground of a lake or ocean

How do sedimentary rocks form? ● Most sedimentary rocks are formed through a sequence of

processes○ Compaction

■ Compaction is the process that presses sediment together ■ When new layers of sediment begin to build up, the older layers

beneath them are pressed together from the weight

How do sedimentary rocks form? ● Most sedimentary rocks are formed through a sequence of

processes○ Cementation

■ Cementation is the process where dissolved minerals crystallize and glue particles of sediment together

What are the 3 major types of sedimentary rock? ● Geologists classify sedimentary rocks according to the type of

sediments that make up the rock○ There are three major groups of sedimentary rocks:

■ Clastic ■ Organic ■ Chemical

What are the 3 major types of sedimentary rock? ● There are three major groups of sedimentary rocks

○ Clastic ■ Clastic rocks are formed when rock fragments are squeezed

together ● Fragments range in size from microscopic particles to large

boulders ■ Clastic rocks are grouped by the size of the fragments ■ Common clastic rocks are sandstone (made from sand on

beaches, ocean floors, riverbeds, etc.) and shale (made from clay particles)

What are the 3 major types of sedimentary rock? ● There are three major groups of sedimentary rocks

○ Organic ■ Organic rocks form where the remains of plants and animals

are deposited in layers ● Coal forms from the remains of swamp plants buried in

water ● Limestone forms in the ocean - when ocean animals die,

their shells pile up on the ocean floor and change into limestone over millions of years

What are the 3 major types of sedimentary rock? ● There are three major groups of sedimentary rocks

○ Chemical■ Chemical rocks form when minerals dissolved in a water

solution crystallize ■ Limestone can also be created this way! When calcite is

dissolved from the ocean animal shells in the sea water, it can form crystal limestone

■ Chemical rocks can also be formed when seas or lake evaporate and leave behind mineral deposits

How are sedimentary rocks used? ● People have used sedimentary rocks throughout history for

building materials and tools ○ Chert was used to make spearheads over 10,000 years ago○ Flint was used to make arrowheads ○ Sandstone and limestone are used as building materials (the White

House is made of sandstone!)