1

What is the Rock Cycle? Rock Cycle

A sequence of events involving the

formation, alteration, destruction, and

reformation of rocks as a result of such

processes as magmatism, erosion,

transportation, deposition, lithification,

and metamorphism!

James Hutton18th Century

• Developed concept to show how rocks and natural physical processes are interrelated.

• Solar energy, gravity, and radio-active heating are the major forces driving the Rock Cycle.

• As a result, cycle will be self-sustaining for thousands of millions of years!

Related to Plate Tectonics

2

• 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.

Becoming an IGNEOUS Rock

• IGNEOUS ROCKS form from molten rock or MAGMA in the sub-surface or from LAVA extruded at the surface.

• The kind of IGNEOUS rock formed depends on WHATwas MELTED and HOW it was COOLED.

• IGNEOUS rocks are classified based on their mineralcomposition and texture (small vs. large crystals)

Any existing rock –IGNEOUS – METAMORPHIC or

SEDIMENTARY – can be subjected to enough heat and/or

pressure causing it to MELT.

IGNEOUS rocks make up BEDROCK

• Granite

• Basalt

• Rhyolite

Becoming a SEDIMENTARY Rock

- The IGNEOUS rock GRANITE can be physically weathered to produce CLAY

and SAND

- These sediments are transported, deposited and lithified to form SEDIMENTARY rocks

- EX: Clay ���� Shale

Sand ���� Sandstone

• The METAMORPHIC rock GNEISS can be physically weathered to produce

CLAY and SAND.

• These sediments are transported, deposited and lithified to form SEDIMENTARY rocks

- EX: Clay ���� Shale

Sand ���� Sandstone

• SEDIMENTARY rocks can be physically weathered to produce sediment that becomes other SEDIMENTARYrocks!

• Chemical weathering dissolves minerals in rocks resulting in precipitates/evaporites like LIMESTONE.

• What forms depends upon composition and environmental factors.

• H20 + CO2 ���� H2CO3

LIMESTONE Formation

3

Becoming a METAMORPHIC Rock

• Pressure, heat and fluids cause pre-existing

rocks or sediments to become METAMORPHIC

rocks.

• SEDIMENTARY rocks

LIMESTONE or DOLOMITEDOLOMITE ����

metamorphic rock MARBLE

• SEDIMENTARY rock

SANDTONE ����

Metamorphic rock QUARTZITE

• SEDIMENTARY rock SHALE ����

metamorphic rock SLATE

• Metamorphic rock SLATE �

metamorphic rock PHYLLITE

• Metamorphic rock PHYLLITE �

metamorphic rock SCHIST

• Metamorphic rock SCHIST �

metamorphic rock GNEISS

Pennsylvania is rich in the following minerals/rocks: iron, lead, cobalt, Copper, Malachite, and Azurite: Copper

limestone, coal

PA Rock Uses

Limestone: Cement

Slate: Roof tiles and flagstones

Clays: Ceramics and bricks

Phosphates: Fertilizers

Coal: Energy

Magnetite, Hematitie, and Goethite: Iron

Galena, Cerussite, and Anglesite: Lead

Sphalerite: Zinc

Cobaltite: Cobalt

Graphite: Lubricants, Pencil Leads

Famous Magnetite deposit in Cornwal, LenanonCounty was worked from 1742 – 1973. Closed due to flooding damage from Hurricane Agnes in 1973.

4

Washington

Co.:

Bituminous

Coal (Energy

to make Steel)

Southern

Illinois:

Fluorite

(Fluxing

Agent)

Minnesota and

Wisconsin: Magnetite

and Hematite (Ore)

England

•Tin was extremely important in the Bronze Age.

•Phoenicians, Greeks, and Romans traded or invaded England for

tin.

•Tin is mixed with copper to make bronze.

•Cassiterate = primary source of tin ore.