Rocks & The Rock Cycle

Unit D, Chapter 2

Introduction Questions

1. How can rocks change?2. What will cause rocks to change?3. How long will it takes rocks to change?4. What will the rocks change/turn into?5. Where do these changes occur?6. What is a cycle?7. What is the rock cycle?

Igneous Rocks

UD, C2, Section 1, pD40-45

Minerals

• Rocks divided into 3 types – how they formed– Igneous– Sedimentary– Metamorphic

• Rocks build landforms– Mountains– Volcanoes, etc.

• Minerals build rocks

Minerals

• Minerals: solid substance with a definite chemical composition and physical structure– Form as crystals• Solids with regular geometric shape

– Shows how atoms are arranged inside of it

– 4000 different minerals (12 common)

Minerals

• Properties: (characteristics)– Hardness • Diamond – Hardest

– Can scratch other substances

• Talc – Softest– Fingernail can scratch it

– Color– Crystal shape– Color of the streak when rubbed on tile– Density (mass ÷ volume)

Formation of Igneous Rocks

• Magma: melted rock inside the Earth– Heat and pressure in mantle melts rock

• Lava: melted rock that reaches Earth’s surface

Formation of Igneous Rocks

• Igneous rock: forms when magma is pushed up from the mantle into the cool crust or onto the surface and hardens into rock– Crystallization: another name for hardening into

rock

Formation of Igneous Rocks

• Intrusive:– Magma hardens under the surface– Cools slowly (millions of years) forming large crystals– Examples: Diorite, Granite, Gabbro

• Landforms:– Shiprock, New Mexico• Magma cooled underground “pluton”• Weathering & erosion wears away softer rock around it• Exposes “batholith”

Formation of Igneous Rocks

• Extrusive:– Lava hardens on the surface– Cools quickly forming small/no crystals– Examples: Rhyolite, Andesite, Basalt, • Obsidian – glassy rock without crystals• Pumice – full of small holes, can float

Uses of Igneous Rocks

• Igneous rocks some of most common on Earth– Granite used as a building material• Looks nice, resists weathering

– Obsidian used for tools, jewelry, and mirrors• Breaks with sharp edges, looks nice, glassy surface

– Pumice used as scouring substance in soaps/cleaners• Can be pounded into powder

– Igneous rocks are the source of many ores• Chromium, platinum, diamond, nickel, copper

– Ore: useful minerals/mixtures or minerals that are mined

Sedimentary Rocks

UD, C2, Section 2 pD48-53

Formation of Sedimentary Rocks

• Mostly found on surface (75%)(5% all crust)• Weathering: process of breaking rock into

smaller pieces– Natural processes:• Flowing water• Moving ice• Freezing & thawing (contraction & expansion)• Growth of plants

• Erosion: movement of sediment to new place

Formation of Sedimentary Rocks

• Deposition: dropping of sediment– Wind or water when it slows down• Slower means less kinetic energy to carry sediment

– Ice when it melts

• Sedimentation: build up of sediment layers over millions of years– Weight of layers compact (packs down) sediments

• Cementation: glues packed particles together

Formation of Sedimentary Rocks

• Two main groups of sedimentary rocks– Clastic rocks: made of sediments that were

weathered, transported, and deposited in layers– Chemical rocks: formed from minerals that were

dissolved in water, came out of solution, and deposited

Clastic Rocks

• Clastic rocks classified by the size of sediments– Fine particles: Shale

• Most common sedimentary rock• Often contain fossil imprints

– Medium particles: Sandstone• Most sandstone contains the mineral: Quartz

– Coarse, pebble-sized particles:• Smooth edges: Conglomerate

– Transported long distances to smooth edges

• Sharp edges: Breccia– Transported short distance, didn’t have time to round edges

Chemical Rocks

• Chemical weathering– Rocks breaks down into chemicals that dissolve

• Like sugar dissolving in tea/coffee

• Chemical rocks form in two ways– Evaporation leaves sedimentary rocks behind

• Layer of salt at the bottom of dried-up lake

– Animal shells or skeletons can also form rocks• Coral take chemicals out of water – make limestone reefs• Shells pile up, compacted, cemented – form Limestone

– Limestone far from coast – clue to where ancient seas were

Uses of Chemical Rocks

• Sedimentary rocks make building materials– Bricks, tile, pottery, china from Shale & Mudstone– Many building made from Sandstone– Plaster made from rock Gypsum– Food seasoned & preserved with Rock salt / Halite– Snow & ice on roads melted with Rock salt / Halite– Important energy reserves – petroleum & natural gas– Farmers use ag lime treat acidic soil from Limestone– Fertilizer made from Potassium salts / Phophate rocks

Uses Sedimentary Rocks

• Fossils most likely to lie in sedimentary rocks– Scientists observe fossils• Piece together information of life long ago

– Dinosaurs

Metamorphic Rocks

UD, C2, S3 pD56-61

Formation of Metamorphic Rocks

• Metamorphic rocks not common on the surface– Form inside Earth’s crust– Forces inside Earth lift them up– Weathering wears away rock on top of them

• Metamorphism: process when any kind of rock is changed into metamorphic rock– Inside Earth– Intense heat & pressure change properties of rocks– Depends on “parent rock” & amount heat and pressure

Formation of Metamorphic Rocks

• Metamorphism occurs under two conditions:– Regional metamorphism• Most common

– Plates collide with tremendous pressure– Rock crumples and folds forming mountains– Metamorphic rock in their centers

– Contact metamorphism• Occurs deep in the crust and under volcanoes

– Magma rises and touches rock– Rock “bakes” changing properties

Formation of Metamorphic Rocks

• Metamorphic rocks classified into two groups– Foliated• Layers or bands you can see

– Gneiss

– Nonfoliated• Do not appear layered

– Marble

Processes That Cause Metamorphism

• Heat most important cause of metamorphism– Deeper in Earth’s crust, the hotter it gets• 20-60°C hotter per kilometer of depth• If rock gets too hot it melts

– Source of igneous rock

• Heat breaks chemical bonds allowing new crystallization

Processes That Cause Metamorphism

• Pressure another cause of metamorphism– Deeper in Earth’s crust, the more pressure there is

• Weight of all rock & soil above rock presses down• Crustal movement squeezes rock & bends it

– Heat softened the rock already making it easier to bend

• Extremely hot water can cause metamorphism– Mineral-rich water near magma (300-500°C)

• Minerals added/taken away from rock– Gold, silver, copper often deposited in these rocks

• Texture & minerals of rock tell how it was formed

Uses of Metamorphic Rocks

• Metamorphic rocks used in parts of buildings– Marble used in statues & public buildings

• Beautiful & durable

– Slate used for roofs, chalkboards, floors, and pavement stones• Splits easily into thin sheets

– Talc used for lubrication, cosmetics, dusting powder• From schist easy to make into a powder

– Graphite used as pencil “lead” & lubricants• Another mineral from some metamorphic schists

The Rock Cycle

UD, C2, S4 pD64-67

The Rock Cycle

• Rock cycle: shows processes where rocks are formed from each other– A way Earth recycles its rocks

• All rock was igneous to begin– Earth was molten rock early in history and it cooled– Wind, water, ice started weathering/eroding rock

• Formed sedimentary rock

– Heat & pressure deep in earth and millions of years• Changed rock to metamorphic rock

– Rocks changing between these three ever since

The Rock Cycle

• Five main groups of processes– Melting:

• All three rock types melt forming magma

– Cooling & solidification: • Magma cools forming igneous rock

– Weathering, erosion, deposition: • All three rock types form sediments that are deposited

– Cementation & compaction: • Sediment is cemented and compacted forming sedimentary rock

– Heat & pressure: • All three rock types changed to metamorphic rock

The Rock Cycle & Plate Boundaries

• Oceanic – Continental Convergent Boundary– Sedimentary rock• Sediment deposited where rivers end

– Metamorphic rock• Igneous & sedimentary rock carried down• Rock melted as it continues to sink• Magma rises in cracks & bakes rock around it

– Igneous rock • Rising or erupting magma cools

How Fossils Form

Additional Slides

How a Fossil Forms

• Most fossils form when living things die.

How a Fossil Forms

• Next, the organism is buried by sediment.

How a Fossil Forms

• The sediment slowly hardens into rock and preserves the shapes of the organisms.

How a Fossil Forms

• The sediment slowly hardens into rock and preserves the shapes of the organisms.