Rocks

Sedimentary, Igneous, and Metamorphic

3 Types of Sedimentary Rocks

• Clastic• Chemical• Organic

Clastic Sedimentary Rock

• Sediments form when rocks are weathered and eroded

• Sediments are moved by wind, glaciers and water

• Most clastic sediments are deposited in the ocean

Clastic Sedimentary Rock

• Sediments are converted into solid sedimentary rock by the processes of compaction and cementation.

Clastic Sedimentary RockCompaction & Cementation

Clastic Sedimentary Rock

Compaction & Cementation

Clastic Sedimentary Rock

• Compaction occurs when the weight of overlying materials compresses the deeper sediments.

• Cementation occurs when soluble cementing materials, such as calcite, silica, and iron oxide, are precipitated onto sediment grains, fill open spaces, and join the particles.

Clastic Sedimentary Rock

• Particle (clast) size is key to type of rock–Gravel is > 2 mm–Sand is 1/16 mm to 2 mm–Mud is < 1/16 mm

• Clay is < 4 um• Silt is > 4 um

Sandstone

Conglomerate

Shale

Chemical Sedimentary Rock

• Chemical sedimentary rocks are made of mineral crystals that formed from chemicals dissolved in water.

• The water in the oceans, lakes, and underground is often full of dissolved minerals and other elements.

Chemical Sedimentary Rock

• When water is so full of elements that not all will fit, some are not able to remain dissolved.

• They come out of solution, or precipitate, forming solid mineral crystals.

• Precipitation is the opposite of dissolving.

Chemical Sedimentary Rock

• Minerals precipitate when some water has been evaporated or when a chemical reaction occurs.

• Evaporation takes only water molecules into the atmosphere so the elements in the remaining liquid water become very concentrated. Eventually, they do not all fit and some precipitate out as mineral.

Chemical Sedimentary Rock

Halite

Gypsum

Limestone

Dolomite

Organic Sedimentary Rock

Coal

– Coal: Bituminous & AnthraciteBituminous

Anthracite

Organic Sedimentary Rock

Coal• Coal is an organic sedimentary rock that has been altered slightly by being compressed and heated.

• It was formed by the rapid burial of large numbers of plants; swamp forest.

• Over time the plant material is compacted so much by the weight of the overlying sediment that it is turned in to rock.

Igneous RocksMagma is the molten rock material below the surface.

•Lower density causes magma to rise toward the surface (compared to the surrounding rock).

• Magma at the surface is lava.

• Igneous rocks are formed from solidified/cooled magma or lava.

• Igneous rocks are made of interlocking crystals

Igneous Rock

Igneous RocksMagma extruded onto the Earth’s surface forms volcanic or extrusive igneous rocks.

Magma that crystallizes within the Earth’s crust forms plutonic or intrusive igneous rock.

Extrusive & Intrusive Igneous Rocks

• Intrusive- Magma under the surface– Coarse-grained (igneous rock)– Magma cools slowly and large crystals grow over a long period of time

– Gabbro, diorite, granite

Extrusive & Intrusive Igneous Rocks

• Extrusive- Lava at the surface– Fine-grained (igneous rock)– Lava cools very quickly, consequently crystals do not have time to grow and develop

– Basalt, andesite, rhyolite, obsidian

Igneous Rocks

Molten rock or magma(1,000-1,200 oC), contains chemical elements.

If the magma begins to cool, elements begin to form chemical bonds within the magma and crystals start to develop.

Igneous RocksRocks that form from magma or lava cooled from high temperatures tend to contain a lot of iron and magnesium but little silica. These rocks are called mafic and tend to be dominated by dark colored minerals such as amphibole and pyroxene (Elements: iron & magnesium).

Igneous RocksWhen magma cools slowly, minerals that form at cooler temperatures dominate the resulting rock. These rocks are called felsic and tend to be light colored with minerals such as feldspar and quartz. (Elements: silicon, oxygen, sodium, potassium, & aluminum)

Igneous Rocks

Igneous Rocks

Igneous Rocks

Classification of Igneous Rocks-Texture: crystal size-Color-Mineral composition

Igneous Rocks

Granite•Felsic•Intrusive

Igneous Rocks

Rhyolite•Felsic•Extrusive

Igneous Rocks

Basalt•Mafic•Extrusive

Igneous Rocks

Gabbro•Mafic•Intrusive

Igneous Rocks

Andesite•Intermediate•Extrusive

Igneous Rocks

Diorite•Intermediate•Intrusive

Igneous Rocks

Other Igneous Rocks• Lava flows• Fragmented magma ejected explosively– Ash plumes– Pyroclastic flows

• Cool and solidify very quickly; no minerals developConsequently they cannot be mafic, intermediate, or felsic

Igneous Rocks

Obsidian•Extrusive

Igneous Rocks

Pumice•Extrusive

Metamorphic Rocks

Metamorphic RocksThe Greek word meta means “change” and morph meaning “shape”.

Metamorphic rocks were previously either sedimentary or igneous rocks, but they have been subjected to very high temperature and pressure. (Below the surface of the Earth)

Metamorphic RocksThe temperature was not high enough to make the rock melt (Metamorphic changes occur as the rock is in solid-state), but it was high enough to allow some crystals to grow, and for the minerals to begin to re-crystallize and thus form a new rock.

As temperature rises, crystal lattices are broken down and reformed with different combinations of atoms. New minerals are formed.

Metamorphic RocksThe types of metamorphismRegional metamorphismContact metamorphism

Contact metamorphism Regional metamorphism

Metamorphic RocksContact metamorphismIn the case of contact metamorphism heat comes from contact with molten magma.-This type of metamorphism has a limited and local effect.

Metamorphic RocksRegional metamorphismWhen rocks are forced toward the mantle during the formation of a mountain range and/or other tectonic activity, regional metamorphism occurs.-Large volumes of rock are altered in this way.

Metamorphic RocksMetamorphism does not take place on the Earth’s surface.

Rocks under the Earth’s surface are under great pressure from overlying rock layers.

Deep burial- as depth increases, in the Earth’s crust, the temperature also increases.

Tectonic forces in the Earth may apply lateral pressure to large volumes of rock.

Metamorphic Rocks

Metamorphic Rocks

Metamorphic RocksMetamorphic rocks have been exposed to the surface of the Earth because erosion has striped away overlying rocks.

So, when we see a large area of metamorphic rocks we know we are looking at the core of an ancient mountain range.

Changes During Metamorphism

Parent rock(protolith)

Low temperature Low pressure

Medium temperature Medium pressure

High temperature High pressure Higher temp.

Higher pressure

shale slate phyllite schist gneiss

MELTING

quartz sandstone quartzite

limestone marble

basalt amphibolite or schist

granite gneiss

Metamorphic RocksChange in metamorphic grade with depth

Increasing Directed Pressure and increasing Temps

Metamorphic RocksFoliated metamorphic rock

Foliation forms when pressure squeezes the flat or elongate minerals within a rock so they become aligned. These rocks develop a platy or sheet-like structure that reflects the direction that pressure was applied in.

Foliation: minerals have been rearranged into visible bands.

Metamorphic Rocks

Increasing Directed Pressure and increasing Temps

Metamorphic RocksDirected Pressure causes rocks to become folded, and minerals to reorient

perpendicular to the stress: “foliation”

Schist

Gneiss

Slate

Metamorphic RocksNon-foliated metamorphic rock

Non-foliated metamorphic rocks do not have a platy or sheet-like structure.

Metamorphic rock that does not show bands.

Marble

Quartzite