Igneous Rocks

Igneous Rocks The root word ignis

comes with the latin word for “fire”

Igneous rocks form from crystallization of magma (below Earth’s surface) or lava (above Earth’s surface)

Igneous Rocks Magma is a slushy

mix of molten rock, gases, and mineral crystals

The main compound in magma is silica (SiO2)

Controls melting point and viscosity how well lava flows

Igneous Rocks It takes

temperatures of 800-1200°C deep within the Earth to melt rocks

The main factors involved in magma formation are: Temperature Pressure Mineral Content Water Content

Igneous Rocks As depth beneath

the Earth increases, pressure increases

Melting point increases because particles are more densely packed

Igneous Rocks

Different substances = Different melting points = Partial Melting

As each group of minerals melts, different elements are added to magma, changing its composition

Igneous Rocks During

cooling, the last minerals to melt are the first to crystallize. This called fractional crystallization.

Why?

Types of Igneous Rocks

Formation Factors Composition What it looks like

Extrusive Cools quickly from lava on Earth’s surface

Exposure to air and moisture

Calcium core surrounded by crystals

Glassy, fine-grained, hard to see crystals

Intrusive Cools slowly from magma below Earth’s surface

Gradual temperature change; no environmental impact

High silica content, salt-rich

Rough texture, coarse-grained, big crystals

Igneous Resources Minerals that contain useful

substances that can be mined for profit are called ores.

Due to fractional crystallization, igneous ore deposits are often found in veins. We mine valuable substances such as gold, silver, lead, and copper.

Pegamites: large veins Kimberlites: small veins

(diamonds)

What do we use igneous rocks for?

Igneous Rock Summary Questions

1. Compare and contrast the process of baking cookies to the formation of igneous rocks:a. How is the dough both similar to and different from

magma?b. Describe the viscosity of the dough that we made in

class.c. How does magma change when it is exposed to

temperature change. How is this similar to and different from how the cookie dough changes when exposed to temperature change?

2. What type of igneous rock are you eating? Describe the texture, hardness, grain size, composition, etc and why it represents that type of igneous rock.

3. Sometimes similar minerals clump together in a rock sample. Do you see this happen in your cookie? Provide a hypothesis for why this might happen.

Sedimentary Rocks

Why did this happen?

How do rocks on the Earth’s surface change?

Weathering= rocks and sediments break down

Erosion= smaller pieces are moved to new locations

Three types:Physical (mechanical)ChemicalBiological

What is physical weathering?

NO changes in composition Size and shape change Factors:

Temperature Frost wedging: water

freezes and expands, cracking rocks

Pressure Exfoliation: pressure of

overlying rocks are removed, underlying rocks can expand

Physical WeatheringTEMPERATURE PRESSURE

What is chemical weathering?

Mineral composition CHANGES

Chemical reaction occurs

NEW minerals form Agents:

Water HydrolysisOxygen OxidationCarbon Dioxide ex:

caveAcid ex: acid rain

What is biological weathering?

Living organism cause changes in rocks or sediment

Ex: tree roots growing around a rock and splitting it

Ex: humans displacing or removing rock surfaces

What affects the rate of weathering?

CLIMATE Chemical weathering is

more common/faster in areas of warm temperatures and high rainfall Ex: “Painted Desert” of

Arizona/New Mexico Physical weathering is

more common/faster in areas of cool, dry climate Ex: NC mountains

What are sediments?

Even though igneous rocks are the most common in Earth’s crust, most of Earth’s surface is covered in sediment.

Sediments: pieces of solid rock material re-deposited on Earth’s surface by forces (wind, water, ice, gravity, precipitation, etc.)

How do sediments become sedimentary rocks?

(Part 1)

Weathered particles get moved downhill (erosion)

Get laid down/sink (deposition)

Deposits become layered (sorting)

Layers stack up on top of each other (burial)

These processes add material to sedimentary basins

How do sediments become sedimentary rocks?

(Part 2)

As burial occurs, layers are subjected to greater heat and pressure

These conditions cause lithification lithos = stone Sediments Sedimentary

Rocks Two steps:

Compaction Cementation

What is a sedimentary basin?

Newest, smallest particles

3rd oldest layer 2nd oldest layer Oldest, largest

particles Depression in Earth’s

crust

What do sedimentary rocks look like?

Bedding! Horizontal layers

Graded bedding Bigger on the bottom

Cross-bedding Slanted layers

How are sedimentary rocks classified?

By formationOrganic sedimentary

rocks (from once living things)

Chemical sedimentary rocks (evaporites)

Clastic sedimentary rocks (loose deposits on Earth’s surface)—Most common

Metamorphic Rocks

Change Form You tell me…what factors cause chemical and physical changes in rocks??

What is contact metamorphism?

What is hydrothermal metamorphism?

Molten rock comes in contact with solid rock High temperature/low

pressure

Hot water comes in contact (reacts with) rock High

temperature/moderate pressure

Deep sea vents/volcanoes

How are metamorphic rocks classified?

Foliated

Non-Foliated

How are metamorphic rocks classified?

Foliated

Non-Foliated

What are porphyroblasts?

New metamorphic minerals grow LARGE while surrounding minerals remain small