Section 6.2 Igneous rocks

The Magma Process to form Minerals (Unit 4)

•Molten (liquid) rock in a magma chamber

At, near or under earth’s surface, RISES

•The magma begins to COOL. The atoms, ions and molecules combine to form various mineral compounds.

•The molecules arrange into an orderly repeating pattern to form CRYSTALS.

quartz

Igneous Rocks form from molten (melted) rock

Magma located

Lava located

Cooling rate is:

Crystals are:

Cooling rate:

Crystals are:

Intrusive igneous rocks

Where:

Extrusive igneous rocks

Where:

Very coarse grains

10 mm or larger

Coarse grains

1 mm -10 mm

Fine-grained

Less than 1 mm

Glassy or gassy

(no crystals grains)

Example rocks: Example rocks: Example rocks: Example rocks:

• The RATE at which the molten magma cools determines the crystal size.

• If the magma cools s-l-o-w-l-y

(under the surface taking hundreds of years)

then the crystals will be…

well-formed

granite

Crystallization of Salol Lab

Slow cooling made large, well-formed

crystals

Quick cooling made small crystals

Group/Sort

Sort the igneous rocks into 3 groups by their crystal size:

large

small

None: glassy or gas holes

Intrusive igneous Rocks

Igneous rock terms to knowIgneous rock terms to know

Magma - Lava

Intrusive – Extrusive

Plutonic – Volcanic

Mafic - Felsic

Course texture - Fine texture

High viscosity – Low viscosity

Porphrytic - Pyroclastic

Igneous Plutons (pg 125)

• Laccolith

• Volcanic neck

• Volcano

• Sill

• Dike

• Batholith

LAVA

Ocean floor

Fissure eruption

Violent pyroclasticeruption

• If the magma reaches the surface, erupts from a volcano as LAVA flows on the surface or erupts underwater, it cools quickly, and the crystals will be small / microscopic / not well-formed

basalt

• If the magma erupts explosively from a volcano and cools at a very fast rate, quickly, then the crystals will…. None

obsidian a volcanic rock, cools instantly. so it has no crystal structure, but a

glass-like structure

EXTRUSIVE

Felsic magma Mafec* magma

Page 121

Feldspar, silica magnesium and iron

Mafic (dark)

• Dark colored minerals:• Magnesium and iron Fe • Olivine, pyroxene,

Hornblende, augite,

biotite

• Less than 50% silica

Felsic (light)

• Light colored minerals:

• Quartz, orthoclase Feldspar

• More than 60% silica

Which has a HIGH viscosity?

honey

water

Resistance to flow

Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?

fine crystals

extrusive,

Felsic:

light-colored

High silica

content

Name this rock – page 124

Classification of Igneous rocksClassification of Igneous rocks

Large, well-formed crystals Large, well-formed crystals ANDAND

small, fine crystalssmall, fine crystals

Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?

course crystals,

intrusiveFelsic:

light-colored

High silica

and feldspar

content

Name this rock – page 124

Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?

NO crystals,

extrusive

Felsic:

(High silica

Content)

Name this rock – page 124

Is this igneous rock intrusive or extrusive?Is it mafic or felsic in composition?

Course AND

Fine crystals,

Intrusive AND

extrusive

Course Mafic crystals

AND

Fine Felsic crystals

Name this rock – page 124

http://www.classzone.com/books/earth_science/terc/content/investigations/es0603/es0603page05.cfm

Porphrytic Texture

The magma started to cool deep in the magma chamber and form large crystals

Then it erupted out of a volcano to the surface and the rest of the magma cooled quickly forming small, fine crystals

FELSIC INTERMEDIATE MAFICColor

Minerals (pr. 703)

Silica percent % % %

Thick or Thin

High or Low VISCOSITY

Fast or Slow moving

Hotter or colder temp.?

Examples: Names of the rocks

Section 6.2 pages 121-122 IGNEOUS ROCK: Textures

Porphyritic rocks begin to crystalize ___________________________, Then quickly harden at the __________________________________ Sketch a diagram of a rock with a porphyritic texture:

Ejected materials:

Extrusive rocks cool and crystalize at the _______________________ Their crystal size is __________________________________________ Examples of extrusive rocks:

Intrusive rocks cool and crystalize ______________________________ Their crystal size is __________________________________________ Examples of intrusive rocks:

After reading page 121-126in your notebook….

Select an igneous rock (2,3,5,6,7,9,11,14)

Rock _______#

Intrusive or Extrusive? ______________

Mafic or Felsic? ______________

Which Family? ______________

Bell workMatch the following terms to their definitions

1. Igneous rock that cools beneath the surface.

2. Igneous rock that contains both large and fine crystals.

3. A batholith and sill are examples.

4. Ash, cinders, and lava that erupt from a volcano.

5. An igneous rock that is both intrusive and extrusive.

Plutonic

Pyroclastics

Porphyrytic

Rock PoemsRock Poems

I am fine-grained

And so light stained.

My color ranges from light gray to pink, which probably makes you think…

rhyolite

This rock is rough and oh so tough.

This rock is not light, but dark as the night.

It’s mafic but not fantastic.

It’s found in the ocean and happens to be extrusive.

basalt

It may be coarse, it may be grainy.

It’s so dark, it makes you zany.

It contains feldspar, augite and olivine.

The sweet look of it is so divine.

What rock is this?

You don’t know?

Take a GUESS, it’s…. gabbro

I am so fineYes, I even shine.

Smooth as glass - didn’t have much time.Got no crystals

Shot out of a volcano like a pistolI’m felsic, but I don’t look it

Started to cool as soon as I reached the topHere’s a hint, I’m an extrusive rock

obsidian

A B C

D E F