What is a Rock?

•Naturally-occurring mixtures of minerals. Sometimes include organic matter.

What is a Rock?

•Rocks are divided into 3 groups based on how they were formed:

•IGNEOUS•SEDIMENTARY•METAMORPHIC

What is the difference between a rock and a

mineral?•Rocks are made up of ONE or

MORE minerals.

Once a rock is formed, does it stay the same rock

forever?• NO!

•Rocks are continually changed by many processes, such as weathering, erosion, compaction, cementation, melting, and cooling

•Rocks can change to and from the three types

What is the process through which rocks

change?• The Rock Cycle—earth materials

change back and forth among the different types of rocks

• No set path a rock takes to become another kind of rock

IGNEOUS

SEDIMENTARY METAMORPHIC

Weathering, Erosion, Compaction, Cementation

Recrystallization

Weathering, Erosion, Compaction, Cementation

Recrystallization

Melting, Solidification Melting,

Solidification

• “Ignis” = Latin for “fire”

• Formed from the cooling of either magma or lava

• The most abundant type of rock

• Classified according to their origin and composition

ORIGIN— Where IGNEOUS rocks are formed

2 TYPES OF IGNEOUS ROCK:1) Below ground = from magma (intrusive igneous rock)

•Usually have LARGE crystal grains (they cooled slowly)

2) Above ground = from lava (extrusive igneous rock)

Usually have SMALL or NO crystals (they cooled too quickly)

Peridotite: Intrusive or Extrusive? Why?

Granite: Intrusive or Extrusive? Why?

Obsidian: Intrusive or Extrusive? Why?

• Formed from sediments (rock fragments, mineral grains, animal & plant remains) that are pressed or cemented together or when sediments precipitate out of a solution.

• These sediments are moved by wind, water, ice or gravity.

• Sedimentary rocks represent 7% of the Earth’s crust, but they cover 70% of the Earth’s surface.

• Sedimentary rocks are fossil-carrying rocks.

What turns sediments into solid rock?

1)Water or wind breaks down and deposits sediment (erosion & deposition)

2)The heavy sediments press down on the layers beneath (compaction)

3)Dissolved minerals flow between the particles and cement them together (cementation)

How can sedimentary layers help us understand the age of

fossils?• As sedimentary

rocks are deposited, they form horizontal layers

• Scientists know that the layers on top (and the fossils in the top layer) are YOUNGER than the fossils in lower layers.

• Rocks that have changed due to intense temperature and pressure

• “Meta” means “change” and morphosis means “form” in Greek

• Igneous, sedimentary and other metamorphic rocks can change to become metamorphic rocks

What occurs in the Earth to change these rocks?

•Pressure from overlying rock layers•High heat, but not enough to melt the

rock•Rocks may be flattened or bent or

atoms may be exchanged to form new minerals.

• *You can think of metamorphic rocks as a squished peanut butter & jelly sandwich in your lunch.

Bill Nye Video

QUESTIONS

1. What are the three types of rocks?2. What type of rocks hold fossils?3. What are the 2 kinds of igneous rocks?4. What kind of igneous rocks are formed below the

earth’s surface?5. What kind of rock has the Grand Canyon formed

in?6. What are rocks made of?7. Will an igneous rock stay an igneous rock

forever?