TThhee RRoocckk CCyyccllee

Prepared by the Michigan Department of Environmental QualityOffice of Geological Survey

What is tWhat is thhee

RRoocckk CCyycclle ?e ?

The RRoocck k CCyycclle e explains how RocksRocks and Natural ProcessesNatural Processes

are related

weathering

melting

pres

sure

, hea

t

Sedimentary Metamorphic

Igneous

is a sequence of events involving the

formation, alteration, destruction, and reformation of rocks as a result of natural processes ...

Glossary of Geology, Bates & Jackson, AGI

RRoocckk CCyycclleeA more traditional definition is:

We will use the graphic seen in the background to help

represent the RRoocck k CCyycclle.e.

There are many ways to show the various relationships between the rocks and

the related natural processes.

let’s review some basic information …

Before we look at the

RRoocck k CCyyccllee

in detail,

The RRoocck k CCyyccllee involves the recognition of three main classes of rocks.

The three rock types are …

CEMETERYCEMETERY METABOLICMETABOLIC

INGENIOUSINGENIOUS

SedimentaryRocks

MetamorphicRocks

IgneousRocks Right?Right?

The eminent 18th century lawyer, doctor, gentleman farmer and founder of modern geoscience,

James HuttonJames Hutton, developed the concept of the RRoocck k CCyyccllee to show how rocks and natural, physical processes are interrelated.

The understanding of the world in the 18th century was different from today …

Hutton knew about solar energy and gravity at the surface. He did not know about

from inside the earth.

As a result, the RRoocck k CCyyccllee

will be self-sustaining for thousands of millions of years.

Solar energy, gravity and radioactive heating are the major forces driving the RRoocck k CCyyccllee.

radioactive heating

How does an antique concept like the RRoocck k CCyyccllee hold up in light of contemporary data and scientific thinking?

Of special interest is Plate Tectonics.

The mantle, crust and surface of the earthcan be thought of as a giant recycling machine;rocks are neither created nor destroyed, but redistributed and transformed from one rock type to another.

IM

S

If you were to ask a geologist what the earth is …

What do you think theresponse would be?

Diagram of the Interior of the EarthCrust

0 to 40 km 0°C

Upper Mantle40 to 670 km

1,000°C

Lower Mantle670 to 2,890 km

2,000°C

Outer Core2,890 to 5,150 km

3,700°C

Inner Core5,150 to 6,370 km

4,300°C

lets move to some of the smallest components of Geology …

Now that we better understand the largest components of Geology …

.

Minerals make up rocks.

Natural compounds and elements combine to form minerals.

Elements combine to form the natural compounds.

Rocks make up the Earth.

There is a hierarchy to the elements of Geology

Atoms make up elements.

Elements can be arranged, based on their identifiable properties, into the Periodic Table

Atomic Theory proposes that all matter is composed of the atoms of about 100 different chemical elements. It further proposes that chemical compounds are formed by the combination of the atoms of different chemical elements.

Only eighteight elements make up over 98%

of the earth’s crust!

Mg

Na

K

OSiAl

FeCa

.

Minerals make up rocks.

Natural compounds and elements combine to form minerals.

Elements combine to form the natural compounds.

Rocks make up the Earth.

There is a hierarchy to the elements of Geology

Atoms make up elements.

What are Minerals? How can we tell what they are?

The identifiable The identifiable

characteristics ofcharacteristics of MineralsMinerals areare

naturally occurring inorganic elements or naturally occurring inorganic elements or compoundscompounds

having an orderly internal having an orderly internal structurestructure

and a characteristic chemical and a characteristic chemical compositioncomposition,

crystal form andcrystal form and

physical properties of a physical properties of a solidsolid

MineralsMinerals combine to form combine to form

RocksRocks

Some RRoocckkss are made up of just one

mineral - like the sedimentary rock salt (made up of the mineral halite) that is mined near Detroit.

Others RRoocckkss are made up of many minerals - like the igneous rock

granite and the metamorphic rock

gneiss, found near Marquette.

Now that some of the basicshave been covered, letsconsider some of the

details about the

RRoocckk CCyyccllee

The RRoocck k CCyyccllee

weathering

Sedimentary Metamorphic

Igneous

Rocks are weathered,eroded,transported,deposited,and lithified to formsedimentary rocks

The igneous rock granite canbe physically weathered to produce clay and sand.

Becoming a SEDIMENTARY ROCK …

Sand can become sandstone.

Clay can become shale

These sediments can be transported deposited and lithified to form sedimentary rocks.

The metamorphic rock gneiss can be physically weathered to produce clay and sand.

Becoming a SEDIMENTARY ROCK …

Sand can become sandstone.

Clay can become shale

These sediments can be transported deposited and lithified to form sedimentary rocks.

Sedimentary rocks can be physically weathered to produce sediments that can become other sedimentary rocks.

Becoming a SEDIMENTARY ROCK …

Chemical weathering dissolves the minerals in rocks. The resulting dissolved compounds could form evaporites like rock salt or rock gypsum or chemical precipitates like some kinds of limestones. What forms depends upon composition and depositional environment factors.

H2O + CO2 H2CO3

2KAlSi3O8+ 2H+ + H2O Al2Si2O5(OH)4+ 2K+ + 4SiO2

Becoming a SEDIMENTARY ROCK …

Sedimentary rocks

include:

sandstone,shale,limestone,rock salt, and rock gypsum.

As the ice advancesit can scour the bedrockand move a lot of material.

When the ice retreats,sediments are deposited and new set of landforms exist.

Glacial deposits

bedrock on which they are resting.

are much youngerthan the

The RRoocck k CCyyccllee

melting

Sedimentary Metamorphic

Igneous

Igneous Rocksform from molten rock or magma in the subsurface or from lava extruded at the surface

Becoming an IGNEOUS ROCK …

When magma cools to a solid it becomes an igneous rock.

Molten rock is called magma.

Any existing rock – igneous, metamorphic or sedimentary - can be subjected to enough heat and or pressure causing it to melt.

The kind of igneous rock formed depends on what was melted and how it cooled.

Igneous rocks are classified based on their mineral composition and texture.

basaltgranite

granodiorite

rhyolite

pegmatite

Igneous rocks include:

pres

sure

, hea

t

Sedimentary Metamorphic

Igneous

The RRoocck k CCyyccllee

Pressure, Pressure, heatheatand fluidsand fluids cause preexistingrocks or sediments to becomemetamorphic metamorphic rocksrocks

Becoming a METAMORPHIC ROCK …

When the prefix meta is applied to a rock name that means that the original rock has been metamorphosed.

If the igneous rock basalt is exposed to sufficient heat and or pressure it can be transformed into the metamorphic rock call metabasalt

Becoming a METAMORPHIC ROCK …

If the sedimentary rock sandstone is metamorphosed it can become the metamorphic rock quartzite.

If the sedimentary rock limestone or dolomite is metamorphosed it can become the metamorphic rock marble.

If the sedimentary rock shale is metamorphosed it can become the metamorphic rock slate.

Becoming a METAMORPHIC ROCK …

If the metamorphic rock phyllite is metamorphosed it can become the metamorphic rock schist.

If the metamorphic rock slate is metamorphosed it can become the metamorphic rock phyllite

If the metamorphic rock schist is metamorphosed it can become the metamorphic rock gneiss.

weathering

melting

pres

sure

, hea

t

Sedimentary Metamorphic

Igneous

The RRoocck k CCyyccllee

The RRoocck k CCyyccllee

does not go in just one direction. Any given rock can go through any part of the cycle any number of times.

DEQ GSD - The Rock Cycle in Michigan - February 2001

weathering

melting

pres

sure

, hea

t

Sedimentary Metamorphic

Igneous

The RRoocck k CCyyccllee

I hope you better understand the RRoocck k CCyyccllee

and what it means.

DEQ GSD - The Rock Cycle in Michigan - February 2001