Chapter 5: RocksSection 1: Classifying Rocks

What are rocks made of?

Rocks are mixtures of minerals and other materials.

Some contain only a single mineral; others contain several minerals (ex. granite = quartz + feldspar + hornblende + mica)

Rock-forming minerals: approx. 20 common minerals that make up most of the rocks of Earth’s crust

Lecture Check 1

Question: What are rocks made of?

Lecture Check 1

Question: What are rocks made of? Answer: Mixtures of minerals and other

materials

Mineral Composition and Color

Color provides clues to the rock’s mineral composition Granite: light-colored rock with high silica content Basalt: dark-colored rock with low silica content

Shape and color of crystals Tests used to identify minerals (e.g. acid test)

Lecture Check 2

Question: How is silica content related to color?

Lecture Check 2

Question: How is silica content related to color?

Answer: High-silica content is associated with lighter color and low-silica content is associated with darker color.

Texture

Texture: look and feel of the rock’s surface Grain: particles of minerals or other rocks,

which give the rock its texture Size: coarse, fine Shape: rounded, jagged Pattern: banded, nonbanded

Lecture Check 3

Question: What are the three things that you can observe about grain?

Lecture Check 3

Question: What are the three things that you can observe about grain?

Answer: size, shape, and pattern

Classifying Rocks Geologists must use color, composition, texture, and

other tests to classify and identify rocks.

How Rocks Form Three groups of rocks based on origin

Igneous: form from cooling of magma or lava Sedimentary: form when particles of other rocks or the remains

of plants and animals are pressed and cemented together; layers buried below the surface

Metamorphic: form when an existing rock is changed by heat, pressure, or chemical reactions; most deep underground

Lecture Check 4

Question: Limestone forms on the ocean floor in tropical environments. What type of rock do you think limestone is?

Lecture Check 4

Question: Limestone forms on the ocean floor in tropical environments. What type of rock do you think limestone is?

Answer: sedimentary

Post-lesson Quiz

1. What type of rock is formed when an existing rock is changed by intense heat and pressure deep underground?

a. sedimentaryb. igneousc. metamorphicd. mineral

Post-lesson Quiz

2. What type of rock is formed from magma or lava cooling?a. sedimentaryb. igneousc. metamorphicd. mineral

Post-lesson Quiz

3. What type of rock forms when particles of other rocks or the remains of plants and animals are pressed and cemented together?a. sedimentaryb. igneousc. metamorphicd. mineral

Post-lesson Quiz

4. What term describes the look or feel of a rock’s surface?a. textureb. grainc. densityd. mass

Post-lesson Quiz

5. Which is not a characteristic that can be used to identify rocks?a. colorb. crystal shapec. reaction to acidd. size of rock