volcanoes erupt and eject a flow of molten rock material, called magma. magma flows when it is hot...
TRANSCRIPT
AIM: WHAT ARE IGNEOUS ROCKS?
FORMATION OF IGNEOUS ROCK Volcanoes erupt and eject a flow of
molten rock material, called magma.
Magma flows when it is hot and becomes a solid when it cools and hardens.
When hot magma cools and hardens, it forms igneous rock.
Why do volcanoes erupt?
Where does the molten material come from?
What comes our of erupting volcanoes?
MAGMA Temperature and pressure in some areas
beneath the Earth’s surface allow for rocks to melt.
Temperature of magma can reach approximately 650 ˚C to 1200 ̊C.
Because the magma is less dense than surrounding solid rock, it is forced upward toward the surface.
When magma reaches the Earth’s surface and flows from volcanoes, it is called lava.
INTRUSIVE ROCKS Rocks that form from magma below the
Earth’s surface are called intrusive igneous rocks.
It takes a long time for intrusive rocks to cool.
Intrusive rocks are found at the surface only after the layers of rock and soil that have once covered them have been removed by erosion.
EXTRUSIVE ROCKS Extrusive igneous rocks are formed as
lava cools on the surface of Earth.
The lava is exposed to air and water.
The lava will cool faster. This prevents mineral grains from growing large.
VOLCANIC GLASS These rocks are cooled so quickly that
few or no mineral grains will form.
Gases may become trapped in the molten material when it cools.
Some of the gases may escape the rock causing holes to form around it.
Examples:Pumice, Obsidian, and Scoria
CLASSIFYING IGNEOUS ROCKS Igneous rocks are classified depending
on how they are formed: IntrusiveExtrusive
DIFFERENT TYPES OF IGNEOUS ROCKS
Basaltic Rocks – Igneous rocks that are dense, dark colored rocks. Rich in iron and magnesium Poor in silica
Granitic Rocks - Igneous rocks that are of a lower density than basaltic rocks and are light-colored. High in silica Found in regions of violent volcanic eruptions
Andesitic Rocks - Igneous rocks have a mineral composition between that of basaltic and granite rocks.
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The violent nature of some volcanic eruptions is partly explained by the composition of the magma that feeds them.