Download WEEK 10: IGNEOUS ROCKS

WEEK 10: IGNEOUS ROCKS
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Igneous rocks are formed by the solidification of magma or lava.
a. Solidification  cooling
Magma and Lava are essentially the same thing:
a. Magma  molten (partially melted) rock below Earth’s surface
b. Lava  molten (partially melted) rock at or above Earth’s surface
Use the rock cycle diagram on p.6 of the ESRT
Igneous Rocks can be broken up into two main categories
a. INTRUSIVE & EXTRUSIVE
INTRUSIVE igneous rocks:
a. Cool slowly underground over 100’s of years  PLUTONIC
b. Because they cool slowly these rocks are large crystals. Their grain size will be larger than
1mm. They will have a coarse or very coarse texture.
EXTRUSIVE igneous rocks;
a. Cool quickly above ground in just minutes  VOLCANIC
b. Because they cooled quickly these rocks have very small crystals. Their grain size is less
than 1mm and they will have a fine texture. Or, if they cooled really fast they might not
have any crystals at all  NON-CRYSTALLINE. If they were cooled super fast they’ll
have a GLASSY texture. Some of these rocks may have gas pockets and have a vesicular
texture.
Be able to read the Scheme for Igneous Rocks Chart on p.6 of the ESRT.
EXTRUSIVE
INTRUSIVE
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Igneous rocks are also categorized by their mineral composition into two main groups:
FELSIC and MAFIC.
a. FELSIC igneous rocks are lighter in color, less dense, and contain minerals with more
ALUMINUM.
i. The minerals that specific to felsic rocks are Potassium Feldspar and Quartz.
ii. These rocks are mostly CONTINENTAL material.
b. Mafic igneous rocks are darker in color, more dense, and contain minerals with higher
concentrations of iron and magnesium (Fe & Mg).
i. The minerals that are specific to mafic rocks are Pyroxene and Olivine.
ii. These rocks are mostly OCEANIC material.
Be able to determine the mineral composition of rocks from the ESRT:
FELSIC
MAFIC
CONTINENT
OCEANIC
The rocks in the middle are made by mixing felsic and mafic materials. These rocks are found
where ocean floor and continents collide. The classic example is the west coast of South
America. The mountains of the Andes are filled with Andesite (hence the name). The lava
from those volcanoes is a mixture of felsic and mafic material.