Ch. 22.3 The Rock CycleRocks: a solid collection of minerals or mineral materials.

Rock Types

Igneous

Sedimentary

Metamorphichttp://www.childrensmuseum.org/geomysteries/faq1.html

Igneous Rocks

• Formed when molten rock cools and solidifies.• As rock cools, minerals in rock cool

The more quickly rock cools less crystals Obsidian has less minerals than granite.

• Extrusive vs. IntrusiveExtrusive - Cools on E’s surface– Examples: Obsidian & Basalt (sea floor)

Intrusive – magma cools while trapped beneath E’s surface. Cooling takes millions of yrs.– Example: Granite (Lots of large crystals)

Obsidian

Basalt

Granite

Devil’s Tower, WY

Volcanic Plug

Sedimentary Rocks

• Formed when pieces of rock or sediment (fragments of older rock & fossils, or living things, & minerals), get squeezed and cemented together.

• Sediments bcm rocks– (1) Layers of sediment get compressed from weight above,

forming rock (LITHIFICATION) – (2) Minerals dissolved in water seep b/w bits of sediment and

CEMENT them together• Named according to size of fragments they contains

– Conglomerate – pebbles & big fragments– Sandstone – sand– Mudstone – fine mud (CAN’T SEE INDIVIDUAL GRAINS)– Limestone – fossils of organisms that live in the water.

Types of Sedimentary RocksA. Clastic: form fr. broken fragments of other

rocks (usu. Held together by cement)Ex.: Conglomorate, sandstone, mudstone

B. Chemical: form fr. minerals that precipitate out of solution.Ex.: Tufas (calcium cabonate rocks)

C. Organic: form as a result of organic (living) processes Ex. :Limestone made from shells of organisms or rocks w/ fossils in them

Tufas (salt towers): Chemical

Conglomerate: Clastic

Limestone Cliffs of Dover: Organic

Sandstone: Clastic

Metamorphic Rock

• Formed when HEAT, PRESSURE, or CHEMICAL PROCEESES w/in E cause changes in the texture and mineral content of rocks (metamorphic = to change forms in Greek)

• Rock undergoes a change w/out melting over millions of yrs.

• Fossils get destroyedExamples:• Limestone + heat + pressure Marble• Mudstone/Shale + heat + pressure Slate

Foliation:

Minerals & crystals in rocks realign into bands in metamorphic rocks.

http://www.uwgb.edu/dutchs/GRAPHIC0/ROCKMIN/RockCycle7.gif

http://www.ltcconline.net/julian/california/cycle.gif

Rock Cycle

Process of events in which rocks can be weathered, melted, altered, and formed over millions of yrs.

Rock Cycle Processes

Weathering: wind & water breaks rocks down into fragments (Makes sedimentary)Cementation: Water “glues” sediment together to make rock

SEDIMENTARY ROCKS: on surface

Weathering / Deposition of Sediments / Cementation (lithification) Sedimentary Rock

IGNEOUS ROCKS: On surface (extrusive) or interior (intrusive)Melting / Cooling & Solidifying Igneous Rock

Metamorphic Rock: Usually inside Earth (@ depths associated w. higher pressures & temps.)

Heat / Pressure Metamorphic Rock

Rock ID Check UpAnswer these questions on lined paper in complete sentences.

• Which rocks were igneous? List # and name.• Which of igneous rocks would be considered EXTRUSIVE?• Which rock was an intrusive igneous? What characteristic can

you observe to confirm that it is intrusive?• Did granite form quickly or slowly? How do you know?• Which rocks were sedimentary? List # and name.• Which sedimentary rocks were clastic?• Which sedimentary rock was organic or chemical?• Which rocks were metamorphic? List # & name.• Shale can turn into slate. What conditions would change shale

into slate? • Which rock (or rocks) could you find fossils in? Support your

answer.