Chapter 3

ROCKSNJCCCS: 5.4 C – Properties of

Earth Materials

What is a Rock?

• A mixture of minerals, mineraloids, glass, or organic matter

• ex. Granite = mica + quartz + feldspar + hornblende + other minerals

3 Rock Types

• Igneous Rocks – form from cooling magma or lava

• Metamorphic Rocks – form from extreme heat and pressure

• Sedimentary Rocks – form from the compaction and cementation of sediment (rock fragments)

Other Key Terms• Magma: molten rock inside the Earth

• Lava: molten rock on the surface of the Earth

• Sediment: smaller pieces of rock (rock fragments)

• Weathering: breaking rocks into sediment

• Erosion: moving sediment from one location to another

• Compaction and Cementation: process of squeezing and gluing sediment into a sedimentary rock

The Rock Cycle

Igneous Rocks

• Igneous Rocks - cooled molten material form the inside the Earth(magma) or out of a volcano (lava)

• - the most common rock on Earth

Igneous Rocks

• B. The Earth’s crust generates great temps (1400), pressures, and radioactive thermal energy

• C. Rocks and Minerals melt to form magma, minerals have different densities and melting pts

Igneous Rocks• D. Magma is less dense than the crust above and forces an escape through volcanoes as lava

• E. Sometimes magma forces upwards but cools before reaching the surface

Classification of Igneous Rocks (1)

• Intrusive Igneous Rocks - those rocks that were formed from cooling magma below the Earth’s surface

• Cool very slowly

• Have large crystals called mineral grains

• Extrusive Igneous Rocks - Rocks that formed from cooling lava on the surface of the Earth

-Cool very quickly

- Have very fine grained texture

IGNEOUS ROCKS – cooled magma or lava

Intrusive igneous rocks have large mineral grains!!!!!

Extrusive igneous rocks have virtually no mineral grains.

Classification of Igneous Rocks (2)

• 1. Basaltic – dense, heavy, dark colored rock, rich in magnesium and iron, most common

• 2. Granitic – light color, less dense, rich in silicon and oxygen

• 3. Andesitic – mineral compositions in between the two, common among Pacific Volcanoes

BASALT

ANDESITE

GRANITE

Igneous Features

(Plutonic) Intrusive Igneous Features

• Magma Chamber is a large underground pool of molten rock found beneath the surface of the Earth.

Intrusive Igneous Features

• Sill is an intrusion of magma that solidifies into a horizontal layer of igneous rock

Intrusive Igneous Features

• Dike is a magma that cuts across rock layers (vertical)

Intrusive Igneous Features

• Batholith is a magma chamber that cools before reaching the surface to form a volcano

Intrusive Igneous Features

• Laccolith is a small magma chamber at shallow depth (roughly lens shaped)

Extrusive Igneous Features

• Volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, volcanic ash and gases to escape from below the surface

• 3 types:• Shield• Composite• Cinder

Extrusive Igneous Features

• Lava Flow – different types of lava depending on the composition and temperature

Extrusive Igneous Features

• Ash and Dust Particles

Extrusive Igneous Features

• Pyroclastic Flow is a fast-moving current of extremely hot gas ( 1,830 °F) and rock which travel away from a volcano at speeds generally as great as 450 mph.

Sedimentary Rocks

• 3 Types of Sedimentary Rocks • 1) Clastic – made from rock fragments

• 2) Chemical – evaporation or precipitation from solution

• 3) Organic – contains fossils

Classification of Sedimentary Rocks

• 1) Clastic

Made from sediments

Chemical – evaporation/precipitation

Organic – contain fossils

Coquina

Fossil-rich limestone

Sedimentary Rocks

Formation of Sedimentary Rocks

• Weathering and erosion makes sediment!!!!

• Glaciers Wind

• Gravity Water

Sediment Sorting

• Clastic Sedimentary Rocks are made of rock fragments.

• Parent Rock – source of rock fragments

Sediment Sorting - As erosional forces lose energy, sediment is deposited largest first-smallest last

Sediment Sorting

• Largest to Smallest• Boulder• Cobble• Gravel• Pebble• Sand• Silt• Clay

Conglomerate

• Pebbles ------------------- Conglomerate

Sandstone

• Sand -------------------- Sandstone

Siltstone

• Silt --------------------- Siltstone

Shale

• Clay ---------------------- Shale

Sediment Sorting

Organic Sedimentary Rock

• Coal – formed from the Remains of plants at the Bottom of a body of water

Limestone – formed from the mixed skeletal remains of marine organisms

Chemical Sedimentary Rock

• Gypsum – easily dissolves in water… gypsum rock forms when the water evaporates and crystallizes

• Halite – (salt) – easily dissolves in water…halite forms when salt water evaporates and crystallizes

Metamorphic Rocks

Metamorphic Rocks

• Metamorphic Rocks - rocks that have changed due to increases in temperature and pressure (the minerals inside them change shape and alignment)

• - igneous, sedimentary, metamorphic rocks can metamorph

• B. Ex. Basalt Schist Gneiss • Shale Slate Phyllite Gneiss• Granite Gneiss

Metamorphic Rocks

Occurs in 2 general ways: •1) Contact Metamorphism•2) Regional Metamorphism

Contact Metamorphism

• As magma pushes through rock layers beneath the Earth…nearby rock change slightly in composition and structure

Regional Metamorphism

• As the Earth’s plates move, the same extreme pressures that build mountains also cause rocks to deform and change in composition

WHAT HAPPENS?

• Heat - (2 sources- magma and depth)

• Minerals within the rock melt and re-crystalize thus changing the composition of the rock

WHAT HAPPENS?

• Pressure – causes space between minerals to close – compacted often causing minerals to recrystalize

2 classifications

• Foliated – banded (layers) of minerals at 90 degree angles to the pressure that caused the metamorphism

• Non-Foliated – no bands or layers (usually composed of only one type of mineral)

Metamorphic Rocks – HEAT AND PRESSURE

FOLIATED = bands of mineral grains NON-FOLIATED = no bands of mineral grains

Rock Classification

• Igneous MetamorphicSedimentary

• Intrusive FoliatedClastic

• Extrusive Non-Foliated ChemicalOrganic

• Basaltic (Mafic)• Andesitic• Granitic (Felsic)

FOSSILS

NJCCCS: 5.4B History of the Earth5.4.12.B.1, 2, 3

Fossils

• Fossil - any naturally preserved evidence of past life

Understanding Decomposition• When an organism dies specialist organisms called decomposers and

detritivores begin consuming its remains.

• Decomposers are usually bacteria and fungi (think sour milk and moldy bread)

• Detritivores are animals like vultures, hyenas, insect larvae, and a host of others (think maggots in a garbage can)

• Most often only the hard tissue of the organism is left behind… bones and teeth, shells, exoskeletons, etc.

• See Video clip – Blue Planet• https://www.youtube.com/watch?v=vQbGk4sHROg&noredirect=1

Fossils Are Rare

• Fossils only form under very special environmental conditions!!!!!!!

• Usually found in sedimentary rocks…why?

• Exceptions: Volcanic ash

3 ways in which fossils form

• 1) Mineral Replacement

• 2) Mostly Unchanged

• 3) Trace

Mineral Replacement

• Underground water removes original material 1 atom at a time and replaces it with minerals.

• An exact copy is created out of the minerals calcite CaCO3 or silica SiO2.

• *Most Common way in which fossils form

• 3 basic types Petrification, Molds, Casts

1) Petrification

• the organism gets totally replaced with minerals

2) Molds

• dead creature is covered with sediments and decays away. The remaining cavity in the shape of the original creature is the fossil = impression

3) Cast

• Minerals from ground water seep into the mold, precipitate out of solution, and a stone shape is the fossil

Mostly Unchanged• Actual original parts of an organism are left behind by several

methods.

• 1) Simple Burial• 2) Frozen• 3) Amber • 4) Mummification• 5) Acidic Peat Bogs• 6) Tar

SPECIAL ENVIRONMENTAL CONDITIONS EXIST THAT PREVENT DECOMPOSITION!!!!

1) Simple Burial

• bones and teeth most often remain…share similar properties to minerals (calcium carbonate)

2) Frozen

• soft parts of mammoths have been found in frozen arctic tundra

Why do we put food in a freezer?

Slows down decomposition!!

3) Amber

• resin or ancient tree sap captured creatures (insects, frogs, etc.)

4) Mummification

• creatures desiccate (dry out) and soft parts remain – salt and or lye prevent decomposition

5) Acidic Peat Bogs

• creatures have been preserved in some wetlands that have environmental conditions that prevent decomposition (lack of oxygen, extreme pH)

6) Tar

• ancient oil seeping from underground trapped creatures. La Brea Tar Pits in California hold bones of mammoths, sabretooth tigers, camels, and more. Tar prevented decomposition.

Trace Fossil Evidence

• Evidence of past life NOT including plant or animal remains

• 1) Footprints

• 2) Burrows

• 3) Borings (holes)

• 4) Coprolites (fossil dung)

Fossil Lab - BE CAREFUL

• Some things look like fossils but really aren’t…called rock features.

• Ripple Marks Geodes Cross Bedding

Common fossils in your lab

• Coprolites Belemite (dung) (Squid)

• Trilobite Stromatolite (colony of bacteria)

(arthropod)

• Ammonite (cuddlefish)