JOURNAL #37How does a volcano work?What are the parts of a volcano?

Refer to page 134 in your book for help

TODAY WE WILL DESCRIBE 3 FACTORS THAT AFFECT WHETHER ROCK MELTS AND CLASSIFY IGNEOUS ROCKS ACCORDING TO THEIR COMPOSITION AND TEXTURE

IGNEOUS ROCKWhen magma cools and hardens,

it forms Igneous Rock.Because minerals crystallize as

igneous rock forms from magma, most igneous rock can be identified as crystalline.

Magma form when rock melts.

IGNEOUS ROCKThe 3 factors that affect whether

rock melts include:TemperaturePressure Pressure of fluids in the rock

TemperatureRock melts when the temperature of

the rock increases to above the melting point of minerals in the rock.

PressureRock melts when pressure is removed

from rock that is hotter than its melting point.

Pressure of fluids in the rockThe addition of fluids generally

decreases the melting point of certain minerals in the rock, which can cause those minerals to melt.

PARTIAL MELTINGDifferent minerals have different

melting points, and minerals that have lower melting points are the first mineral to melt.

The process by which different minerals in rock melt at different temperatures is called partial melting.

FRACTIONAL CRYSTALLIZATION

Opposite of partial meltingChemicals in magma combine to

form minerals, and each mineral has a different freezing point.

As minerals freeze (crystallize) at different times, those chemicals are removed from the magma.

The removal of different minerals as magma cools is called fractional crystallization.

TEXTURES OF IGNEOUS ROCKS

Igneous rocks are classified according to where magma cools and hardensIntrusive Igneous Rock- rock

formed from the cooling and solidification of magma beneath Earth’s surface

Extrusive Igneous Rock- rock that forms from the cooling and solidification of lava at the Earth’s surface

TEXTURES OF IGNEOUS ROCKSThe texture of igneous rock is determined

by the size of the crystals in the rock.The size of the crystals is determined by

the cooling rate of the magma.Examples:

Coarse-Grained Igneous Rock- large crystalsGranite

Fine-Grained Igneous Rock- small crystalsBasalt, Rhyolite

Porphyritic Igneous Rock- mixture of large and small crystalsObsidian, Pumic

COMPOSITION OF IGNEOUS ROCKS

The mineral composition of an igneous rock is determined by the chemical composition

Felsic Rock- describes magma or igneous rock that is rich in felspars and silica and that is generally light in color. Examples: granite, pumice

Mafic Rock- describes magma or igneous rock that is rich in magnesium and iron and is generally darker in color.Examples: Basalt

Intermediate Rock- lower proportions of silica than rock sin the felsic familyand higher proportions of silica than rock sin the mafic familyExamples Diorite and Andesite

EXTRUSIVE IGNEOUS ROCK STRUCTURES

Igneous rock masses that form on the Earth’s surface are called Extrusions.

A volcano is a vent through which magma, gases or volcanic ash is expelled.

When a volcanic eruption stops, the magma in the vent may cool to form rock.

The soft parts of the volcano are eroded by wind and water.

The solidified central vent is called a volcanic neck.

YOU’RE ASSIGNMENT:

Work in PAIRS to complete Igneous Rock Review

Use notes and pages 129-134 in your book