The Rock Cycle Prepared by the Michigan Department of Environmental Quality Office of Geological Survey

What is the Rock Cycle ?

The Rock Cycle explains how Rocks and Natural Processes are related weathering Sedimentary Metamorphic melting pressure, heat Igneous

Glossary of Geology, Bates & Jackson, AGI A more traditional definition is: Rock Cycle 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

We will use the graphic seen in the background to help represent the Rock Cycle. There are many ways to show the various relationships between the rocks and the related natural processes.

Why study the rock cycle?

Before we look at the Rock Cycle in detail, let’s review some basic information …

The three rock types are … The Rock Cycle involves the recognition of three main classes of rocks. The three rock types are …

CEMETERY Sedimentary Rocks Metamorphic Rocks METABOLIC Igneous Rocks INGENIOUS Right?

Sedimentary Rock The three different forms of sedimentary rock are: Clastic= mechanical weathering Mechanical weathering refers to pressure and expanding/contracting. Chemical sedimentary rocks= when dissolved materials precipitate from solution. Organic sedimentary rocks= which form from animal/plant debris. Are formed by the accumulation of sediments over a long period of time.

Igneous Rock The three different forms of Igneous rock are: Intrusive= Formed from magma that cools and solidifies within the crust of a planet, surrounded by pre-existing rock. Magma cools slowly and, as a result, these rocks are coarse grained. Extrusive= formed at the crust's surface as a result of the partial melting of rocks within the mantle and crust. Cool and solidify quicker than intrusive igneous rocks. Hypabyssal= formed at a depth in between the plutonic and volcanic rocks. formed through the cooling and solidification of magma or lava.

Metamorphic Rock The two different forms of Metamorphic rock are: Foliated= Non- Foliated has undergone transformation by heat, pressure, or other natural agencies. Foliated= = a layered or banded appearance that is produced by exposure to heat and directed pressure.

The eminent 18th century lawyer, doctor, gentleman farmer and founder of modern geoscience, James Hutton, developed the concept of the Rock Cycle to show how rocks and natural, physical processes are interrelated. Hutton perceived that this sedimentation takes place so slowly that even the oldest rocks are made up of, in his words, “materials furnished from the ruins of former continents.” The reverse process occurs when rock exposed to the atmosphere erodes and decays. He called this coupling of destruction and renewal the “great geological cycle,” and realized that it had been completed innumerable times.

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

James Hutton’s Theory of Geologic Movement Siccar Point in Ireland Hutton perceived that this sedimentation takes place so slowly that even the oldest rocks are made up of, in his words, “materials furnished from the ruins of former continents.” The reverse process occurs when rock exposed to the atmosphere erodes and decays. He called this coupling of destruction and renewal the “great geological cycle,” and realized that it had been completed innumerable times.

Hutton knew about solar energy and gravity at the surface. He did not know about from inside the earth. radioactive heating Solar energy, gravity and radioactive heating are the major forces driving the Rock Cycle. As a result, the Rock Cycle will be self-sustaining for thousands of millions of years.

How does an antique concept like the Rock Cycle hold up in light of contemporary data and scientific thinking?

Of special interest is Plate Tectonics.

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

If you were to ask a geologist what the earth is … What do you think the response would be?

Diagram of the Interior of the Earth Crust 0 to 40 km 0°C Upper Mantle 40 to 670 km 1,000°C Lower Mantle 670 to 2,890 km 2,000°C Outer Core 2,890 to 5,150 km 3,700°C Inner Core 5,150 to 6,370 km 4,300°C

Now that we better understand the largest components of Geology … lets move to some of the smallest components of Geology …

There is a hierarchy to the elements of Geology Atoms make up elements. There is a hierarchy to the elements of Geology Elements combine to form the natural compounds. Natural compounds and elements combine to form minerals. . Minerals make up rocks. Rocks make up the Earth.

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

Only eight elements make up over 98% of the earth’s crust! Na Mg Al Si K Ca Fe Only eight elements make up over 98% of the earth’s crust!

What are Minerals? How can we tell what they are? Atoms make up elements. There is a hierarchy to the elements of Geology Elements combine to form the natural compounds. Natural compounds and elements combine to form minerals. . Minerals make up rocks. What are Minerals? How can we tell what they are? Rocks make up the Earth.

The identifiable characteristics of Minerals are naturally occurring inorganic elements or compounds having an orderly internal structure and a characteristic chemical composition, crystal form and physical properties of a solid

Minerals combine to form Rocks

Some Rocks are made up of just one mineral - like the sedimentary rock salt (made up of the mineral halite) that is mined near Detroit. Others Rocks are made up of many minerals - like the igneous rock granite and the metamorphic rock gneiss, found near Marquette.

Now that some of the basics have been covered, lets consider some of the details about the Rock Cycle

The Rock Cycle weathering Sedimentary Metamorphic Igneous Rocks are weathered, eroded, transported, deposited,and lithified to form sedimentary rocks

Becoming a SEDIMENTARY ROCK … The igneous rock granite can be physically weathered to produce clay and sand. These sediments can be transported deposited and lithified to form sedimentary rocks. Clay can become shale Sand can become sandstone.

Becoming a SEDIMENTARY ROCK … The metamorphic rock gneiss can be physically weathered to produce clay and sand. These sediments can be transported deposited and lithified to form sedimentary rocks. Clay can become shale Sand can become sandstone.

Becoming a SEDIMENTARY ROCK … Sedimentary rocks can be physically weathered to produce sediments that can become other sedimentary rocks.

2KAlSi3O8+ 2H+ + H2O  Al2Si2O5(OH)4+ 2K+ + 4SiO2 Becoming a SEDIMENTARY ROCK … H2O + CO2  H2CO3 2KAlSi3O8+ 2H+ + H2O  Al2Si2O5(OH)4+ 2K+ + 4SiO2 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.

Sedimentary rocks include: sandstone, shale, limestone, rock salt, and rock gypsum.

As the ice advances it can scour the bedrock and move a lot of material. When the ice retreats, sediments are deposited and new set of landforms exist.

Glacial deposits are much younger than the bedrock on which they are resting.

The Rock Cycle melting Sedimentary Metamorphic Igneous Igneous Rocks form from molten rock or magma in the subsurface or from lava extruded at the surface

Becoming an IGNEOUS ROCK … Any existing rock – igneous, metamorphic or sedimentary - can be subjected to enough heat and or pressure causing it to melt. Molten rock is called magma. When magma cools to a solid it becomes an igneous rock. 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.

Igneous rocks include: granite basalt rhyolite granodiorite pegmatite

The Rock Cycle pressure, heat Sedimentary Metamorphic Igneous Pressure, heat and fluids cause preexisting rocks or sediments to become metamorphic rocks

Becoming a METAMORPHIC ROCK … If the igneous rock basalt is exposed to sufficient heat and or pressure it can be transformed into the metamorphic rock call metabasalt When the prefix meta is applied to a rock name that means that the original rock has been metamorphosed.

Becoming a METAMORPHIC ROCK … If the sedimentary rock limestone or dolomite is metamorphosed it can become the metamorphic rock marble. If the sedimentary rock sandstone is metamorphosed it can become the metamorphic rock quartzite. If the sedimentary rock shale is metamorphosed it can become the metamorphic rock slate.

Becoming a METAMORPHIC ROCK … If the metamorphic rock slate is metamorphosed it can become the metamorphic rock phyllite If the metamorphic rock phyllite is metamorphosed it can become the metamorphic rock schist. If the metamorphic rock schist is metamorphosed it can become the metamorphic rock gneiss.

DEQ GSD - The Rock Cycle in Michigan - February 2001 weathering melting pressure, heat Sedimentary Metamorphic Igneous The Rock Cycle 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

DEQ GSD - The Rock Cycle in Michigan - February 2001 weathering melting pressure, heat Sedimentary Metamorphic Igneous I hope you better understand the Rock Cycle and what it means. DEQ GSD - The Rock Cycle in Michigan - February 2001