Rocks and Their Origins

Petrologic Classification

Dynamic Earth Processes.

Objective- Identify and describe the three classes of rocks.

California Science Standard (3a)- Students know how to explain the properties of rocks based on the physical and chemical composition which they formed, including plate tectonics processes.

Chapter 6-1 What are Rocks?

Rocks- mixture of minerals, generally cemented together.*All rocks are made up of one or more minerals.

Petrologist- (petro is the Greek word for rock.) Earth science specialists who study rocks and minerals and their origin.

Chapter 6-1 Petrologic Cycle (rock cycle)

Rock cycle- series of natural processes by which rocks are slowly changed from one kind of rock into another kind of rock.*It shows the ways that one rock type is changed to another.

Intrusive andExtrusive changesin rock types.

Classification Of Rocks

* Classification- is the grouping of objects by certain characteristics. Scientist classify objects to make them easier to study.

* Petrologist classify rocks based on how they form.

• Igneous rock- rock formed by the crystallization of hot molten rocks or minerals.

Chapter 6-2 How are igneous rocks formedObjective- Identify two ways that igneous rocks are

formed.Molten Rock- melted rocks and minerals.Magma- molten rock inside the earth.* The cooling and hardening of molten rock produces

rocks of igneous classification.Pluton- large body of igneous rock that can form into

different shapes when magma cools inside the Earth’s crust. Aka- igneous intrusions.

* Igneous rocks that form here are classified as intrusive.Intrusive- igneous rocks that form on the inside of the

Earth from cooling magma.Lava- magma that reaches the Earth’s surface.* Rocks that cool on the outside of the Earth from lava are

called extrusive. Extrusive- igneous rocks that form on the outside of the

Earth from cooling lava.

Where igneous rocks form?

Chapter 6-2 How are igneous rocks classified?Objective- Identify and describe igneous rocks by

their minerals and textures.*Igneous rocks are made up of aggregates

(combinations) of minerals. *Six common igneous rock forming minerals;

Quartz, Mica, Amphibole, Feldspar, Olivine, Pyroxene.

Igneous Rock ClassificationCrystal Size

* Crystal size in an igneous rock depends on the rate of cooling.

* Large crystals form from slow cooling.* Small crystals form from fast cooling. Texture- size, shape and arrangement of a rocks crystals. • Igneous rocks are classified based on their texture.• Coarse texture- igneous rocks with large crystals.• Fine Grain texture- rocks that have small crystals.• Glassy- rocks that cool so fast they have no specific crystals.• Porphyry- rock with a set of different sized crystals.

Igneous MatrixIgneous Rocks

Intrusive (Acid magma) High silica, thick slow flowing,

Extrusive (basic lava)Low silica, hotter,faster flowing

Slow Cooling

Large crystals

Coarse texture

Fast Cooling

Small crystals

Fine grain texture, glassy

Light colored minerals

(Quartz, Plagioclase Feldspar)

Light colored rocks (granite)

Dark colored minerals

(hornblende, dark mica, augite)

Dark colored rocks (basalt)

Sedimentary Rocks

Objective- Describe two ways that sedimentary rocks are formed.

Sediment- rock particles carried and deposited by water, wind, or ice.

Sedimentary- rocks made from the fragments of existing rocks or organic remains.

Chapter 6-3 How are sedimentary rocks formed?

*Most sedimentary rocks are formed in water.*Sediments are deposited in layers or beds

called strata.Deposition- the release of rock fragments into layers.Stratification- layering of rock fragments.

* As the layers thicken, they become compressed.

* Water containing dissolved minerals seeps into the layers and between rock particles, cementing the particles together.

Cementation- minerals when evaporated and left behind bond sedimentary particles together.

Lithification- the creation of solid rock layers through cementation.

Sedimentary formation continued.

Chapter 6-3 Continued.Sedimentary rocks from living things.

* When oceanic animals die they sink to the bottom of the ocean floor.* They get buried, compacted and cemented together to form organic sedimentary rocks.

Organic sedimentary- rocks made from the remains of plants and animals.

Chapter 6-3 How are sedimentary rocks classified?

Objective- Identify and describe the two main groups of sedimentary.

There are two main groups of sedimentary rocks;Clastic rock- sedimentary rock made up of

fragments of existing rock.* Fragments of existing rock are carried by wind,

water and ice.* They are classified according to their sizes and

shapes.Sorting- separation of rock fragments by size.

Clastic Sedimentation

Conglomerate

Chapter 6-3 continued.• Nonclastic Rock- sedimentary rock made up of

dissolved minerals or the remains of once living things.

• Chemical- rocks formed from dissolved minerals.• Precipitants- chemical sedimentary rocks formed when

minerals fall out of solution.• Evaporite- chemical sedimentary rocks formed when

minerals are left behind after evaporation.

Chemical Sedimentation

Precipitant Evaporite(Limestone) (Halite)

Limestone Formations

Dissolved minerals that drip from the tops of caves form chemical deposits.

Stalagmites Stalactites

Organic Sedimentary• Story of Coal

• Peat- Loose, partially decomposed plant material.• Lignite (brown coal)- more compacted, partially decomposed

plant matter.• Bituminous (soft coal)- Highly compacted decaying material

that consist of 85% carbon.• Anthracite (hard coal)- Metamorphosed bituminous coal, 90-

95% pure carbon.

Types of Coal Peat Lignite

Bituminous Anthracite

Sedimentary Matrix

Sedimentary

Clastic Chemical OrganicFragments Chemical Action RemainsSorting Precipitant Evaporite CoalStratification Falls Out Left behind Peat

Cementation Limestone Rock Salt Lignite

Lithification Bituminous

Conglomerate Anthracite Sandstone

Shale

Chapter 6-4 How are metamorphic rocks formed?Objective- Describe two ways in which

metamorphic rocks form.Metamorphism- meta (change), morph (form)Rocks that change in form as a result of heat and

pressure.

*Metamorphic Rock is formed by the effects of heat and pressure upon igneous and

sedimentary rocks. 

Chapter 6-4 Metamorphism

*Minerals in rock change chemically when heated. Minerals go through chemical changes at temperatures between 200°C and 800°C. Above 800°C they change into magma or molten rock.

* Forces within the Earth cause pressure, which changes a rocks mineral form.

Chapter 6-4 How are metamorphic rocks classified? Dynamic Metamorphism

Objective- Explain the difference between foliated and nonfoliated metamorphic rocks.

*Metamorphic rocks are classified based on their texture; Foliated and nonfoliated.

Foliated- texture of a metamorphic rock that has mineral crystals arranged in bands.

Granite Gneiss

*Foliated rocks tend to break along their mineral crystal bands.• These rocks are formed under extremes of pressure and

some heat.

Chapter 6-4 Thermal Metamorphism

Nonfoliated- texture of a metamorphic rock that does not have mineral crystals arranged in bands.* nonfoliated rocks do not break in layers. * Formed under great heat and little pressure, through recrystallization.

Limestone Marble

Metamorphic Matrix

Metamorphic

Dynamic (Regional) Thermal ( Contact)Foliated NonfoliatedPressure / little heat High temperature / little

pressurePlate Tectonics Volcanoes / Plate

tectonicsMineral Banding Recrystallization

Sandstone - Quartzite Limestone - MarbleShale – slateSlate - schist