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Interlude B:

Rock Groups

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Rocks are:

Coherent

Naturally occuring

Aggregates ofminerals or masses of

glass

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How are rocks held together?

Grains are heldtogether by cement

A. Clastic rocks

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How are rocks held together?

Crystals interlock

B. Crystalline rocks

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How are rocks held together?

Form as a continuousmass

Grains welded together

while hot

C. Glassy rocks

http://www.es.ucl.ac.uk/schools/Glossary/obsidian.jpg

obsidian

Welded volcanic ash

http://darkwing.uoregon.edu/~dogsci/2/kays

/313/igfig45.jpg

http://www.nio.org/userfiles/image/projects/photomicrograph_1a.jpg

Volcanic

glass

Olivine

crystal

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Rocks are classified based on

how they form.

Solidification of molten rock

A. Igneous rocks

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Rocks are classified based on

how they form.

Pre-existing rocks break up, then grains

are cemented together

B. Sedimentary rocks

Darragh McDonagh (Geological Survey of Ireland)

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Rocks are classified based on

how they form.

Precipitation of mineral crystals

(evaporites)

B. Sedimentary rocks

http://www.travelvivi.com/wp-content/uploads/2009/12/Dead-Sea.jpg

Creative Commons / Wilson44691

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Rocks are classified based on

how they form.

Pressure and temperature cause solid

state changes

C. Metamorphic rocks

http://geophysics.ou.edu/geol1114/notes/met_rx/mica_garnet_schist.jpghttp://w

ww.nvcc.edu/home/cbentley

/gol_135/sideling_hill/images

/shale.JPG

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For each rock type, other characteristics are NB

Grain size and shape

Composition (elements, minerals)

Igneous rocks Sedimentary rocks

Metamorphic rocks

NB = important (nota bene)

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For each rock type, other characteristics are NB

Texture

E.g., smallest to largest

E.g., alignment

Igneous rocks Sedimentary rocks

Metamorphic rocks

NB = important (nota bene)

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For each rock type, other characteristics are NB

Layering

E.g., Bedding

Igneous rocks Sedimentary rocks

NB = important (nota bene)

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For each rock type, other characteristics are NB

Layering

Foliation

Metamorphic rocks

NB = important (nota bene)

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Thin sections (photomicrographs) are a way to

look at microscopic details

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Thin sections (photomicrographs) are a way to

look at microscopic details

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Interlude C:

Rock Cycle

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8-23 Rock cycle: materials move from one rock

type to another

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8-24 How does this work?

Igneous rocks form

Sedimentary(from igneous rocks igneous

igneous

Sedimentary, metamorphic,

igneous rocks are melted

Plates collide

Ocean crust

recycled into

mantle

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8-25 How does this work?

igneous

sedimentary

metamorphic

(sedimentary and igneous rocks

heated and compressed)

(Sedimentary, metamorphic,

igneous rocks have been eroded)

Plates collide and lock

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8-26 How does this work?

sedimentary

igneous

(Sedimentary, metamorphic,

igneous rocks have been eroded)

metamorphic

Plates stop moving, erosion happens

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8-27 How does this work?

Igneous rocks forming

(Sedimentary, metamorphic,

igneous rocks are being melted)

A rift forms, plates move apart