rocks chapter 10. rocks & the rock cycle magma is the parent material for all rocks there are 3...

RocksRocks

Chapter 10Chapter 10

Rocks & the Rock CycleRocks & the Rock Cycle

• Magma is the parent material for all rocks

• There are 3 major types

• Any type can be changed into any of the other types through a series of changes called the rock cycle

3 Major Rock Types3 Major Rock Types

• Three major types– Igneous = magma cools & hardens– Sedimentary = sediment is deposited and

hardens after being compressed & cemented.– Metamorphic = forces such as extreme heat

and pressure and chemical processes change the form of existing rock.

The Rock CycleThe Rock CycleOverviewOverview

• Hardened magma cools -> igneous rock

• Igneous rock breaks down into sediments -> sedimentary rock

• Sedimentary rock subjected to extreme heat/pressure -> metamorphic rock

• Metamorphic rock under extreme heat/pressure -> melt into magma (start over)

The Rock Cycle (cont)The Rock Cycle (cont)

• Rock does not always make it through entire cycle– Igneous rock not exposed to surface will

never become sediment – may go directly to metamorphic

– Igneous and sedimentary may melt directly into magma

– All 3 types may form sediments when exposed

The Rock CycleThe Rock Cycle

Igneous RockIgneous Rock

• Two types = classified by where magma cools– intrusive = cool deep below crust

• May “intrude” into other rock layers• Cools slowly

– extrusive = lava cooling on surface• Cools rapidly

Igneous Rock (cont)Igneous Rock (cont)

• Texture determined by rate of cooling– Intrusive = cools slowly

• Course-grained texture• Ex: granite

– Extrusive = cools rapidly• Little time for crystal formation• Fine-grained texture• Ex: basalt

Igneous Rock (cont)Igneous Rock (cont)• Some extrusive rock cools slowly at

first then more quickly as it nears the surface– Produces both large and small crystals– Porphyry

• Extremely rapid cooling produces rock without crystals

• Gases escaping during rapid cooling may form small bubbles in rock


• Composition of igneous rock is determined by chemical composition of magma.

• 3 Families – based on composition– Granite– Basalt– Diorite


• Granite Family– Felsic magma – high silica– Light color– Main minerals = orthoclase feldspar & quartz– Ex: granite (intrusive)

rhyolite and obsidian (extrusive)


• Basalt Family– Mafic lava = low silica, high iron– Dark color– Main minerals = plagioclase feldspar and

augite– Ex: basalt & gabbro


• Diorite Family– Medium colored– Main minerals = plagioclase feldspar,

hornblende, augite, and biotite.– Little or no quartz– Ex: diorite & andesite

Igneous Rock StructuresIgneous Rock StructuresIntrusions = undergroundIntrusions = underground

• Batholith • Largest (cover over 100km²)• Form cores of many mountains

• Stock• Similar to batholith but cover less area

• Laccolith• Magma pushes overlying rock layer into an arc• May form dome mountains

• Sills• Sheet of magma flows between layers of rock (horizontal)

• Dikes• Magma flows upward through fractures and cut across rock

layers vertically

Igneous IntrusionsIgneous Intrusions

Igneous Rock StructuresIgneous Rock StructuresExtrusions = at surfaceExtrusions = at surface

• Volcanic neck – softer parts of volcanic cones wear away exposing solidified rock in vent.

• Many are simply flat lava flows

• Lava plateaus – lava flows out long cracks in the surface

• Cover vast areas• Fill in valleys and cover hills to form flat plateaus

Igneous ExtrusionsIgneous Extrusions

Sedimentary RockSedimentary Rock• Compaction and cementation form

sedimentary rock.– Compaction – weight of overlying sediments

causes pressure that squeezes air and water out of sediments

– Cementation – water carries dissolved minerals through sediments which provide a cement to hold fragments together.

• Sedimentary rocks are classified by the kind and size of their sediments.

Sedimentary Rock (cont)Sedimentary Rock (cont)• Clastic sedimentary rocks

– Rock fragments are carried by wind, water and ice become compacted and cemented together = classified by size

– Conglomerate = rounded, gravel-sized pebbles cemented by minerals

– Breccia = gravel-sized fragments (angular with sharp edges)

– Sandstones are made up of sand-sized grains• Major component = quartz• Many are porous enough to allow liquids (water,

crude oil) to move through.– Shale consists of clay-sized particles

• Usually pressed into flat, “flakey” layers

Sedimentary Rock (cont)Sedimentary Rock (cont)

• Chemical Sedimentary Rock– Forms from minerals once dissolved in water– Minerals may precipitate out due to

temperature changes– Evaporites form when water evaporates and

leaves minerals behind

Sedimentary Rock (cont)Sedimentary Rock (cont)

• Organic Sedimentary Rock– Forms from remains of living things– Coal forms from dead plant remains buried

and compacted– Limestone forms from the shells of marine

organisms that use calcite• Chalk is limestone made of shells of one-celled

marine organisms

Sedimentary Rock FeaturesSedimentary Rock Features• Stratification = layering = occurs

when type of sediment changes– May be due to change in river

current, sea level, etc.– Thickness of layers (beds)

depends on how long the sediment is deposited

– Most water-deposited layers are horizontal

– Wind-deposited layers may exhibit cross-bedding

– Graded bedding = different kinds & sizes of material are deposited in the same layer as they settle out.

Sedimentary Rock Features (cont)Sedimentary Rock Features (cont)• Ripple marks

– Form from action or wind or water on sand.

• Mud cracks– Muddy deposits dry and

shrink causing shrinking• River flood plains, dry lake

beds• When area floods new deposits

fill in and preserve the cracks.

Sedimentary Rock Features (cont)Sedimentary Rock Features (cont)

• Fossils – The remains or traces of ancient plants and animals– Are preserved in sedimentary rock when remains are

buried– Harder parts may remain but most often it’s only the

impression

Sedimentary Rock Features (cont)Sedimentary Rock Features (cont)

• Concretions– Lumps or nodules of rock with a

composition different from the main rock body

– Precipitated minerals build up around existing rock

– Geodes = groundwater deposits dissolved quartz or calcite inside a cavity and crystals form

Metamorphic RockMetamorphic Rock

• Changing from one type of rock to another by heat, pressure and chemical processes = metamorphism– Minerals may change into other chemicals– Minerals may change size, shape, or separate

into bands (layered look)

– Hot fluids in magma may change mineral composition by dissolving some minerals and adding others

Metamorphic Rock (cont)Metamorphic Rock (cont)

• Two types of metamorphism:– Contact metamorphism

• Hot magma is near or touching rock• Changes structure and/or mineral composition• May also include hot chemical fluids working through

fractures

– Regional metamorphism• Occurs over large areas during tectonic activity• Plates moving against each other causes tremendous heat

and pressure at the edges – causes chemical changes in rock minerals

• Most metamorphic rock is formed this way.


• Classification is according to structure– Foliated

• Visible parallel bands• Extreme pressure flattens mineral crystals into

bands• Minerals of different densities may separate into

bands -> alternating light and dark


• Common foliated rocks– Slate

• Pressure on shale produces thin layers that split into sheets

– Schist• Pressure on slate – courser

grained

– Gneiss• Intense heat and pressure on

schist -> minerals separate into bands of different densities

Metamorphic Rock (cont)Metamorphic Rock (cont)• Unfoliated

– Rocks do NOT have bands of crystals• Quartzite – sandstone is highly compacted

• Marble – compression of limestone

rocks chapter 10. rocks & the rock cycle magma is the parent material for all rocks there are 3...

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