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IGNEOUS ROCKS
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Igneous means, “() formed”
Solid Rock Igneous means, “() formed”
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() is molten (liquid) material () the surface of Earth.
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MAGMA VS. LAVA Magma – molten material () the surface of the Earth
Lava – molten material () earth’s surface
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The () cooled and solidified INSIDE Earth into an intrusive igneous rock
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Molten (liquid) material at the surface of Earth is called ().
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Extrusive rock is also called () rock.
The lava cooled and solidified () it exited Earth into an extrusive igneous rock
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When () or () cools it () (a fancy word for something becoming a solid). When this happens crystals form. Solidification can also be called (). The rocks crystals are minerals.
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The size of the mineral crystals that form in an igneous rock depend on the ( ).
As a general rule, the () a rock takes to cool, the () the mineral grains will become. As a result…
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COOLED FAST at the surface, so either there are no () or they are so () they are not visible.
COOLED SLOW () the surface, so () minerals have time to grow.
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Lava exposed at the surface cools very fast so no minerals can grow, it looks () or has ().
Earth’s surface Deep in Earth’s crust
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If it cools () the surface it grows () mineral crystals but not big enough to see.
Earth’s surface Deep in Earth’s crust
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As you get deeper into Earth’s crust magma cools slower
As you get deeper into Earth’s crust magma cools slower. This allows () crystals to grow. Earth’s surface Deep in Earth’s crust
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Really deep in Earth’s crust magma cools really, really ()
Really deep in Earth’s crust magma cools really, really (). This allows mineral crystals to grow really, really (). Earth’s surface Deep in Earth’s crust
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Which is the intrusive rock and which is the extrusive rock?
Pop quiz hot shot!!! Which is the intrusive rock and which is the extrusive rock? Extrusive Intrusive Fine grained Large crystals Basalt Granite
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Scheme for Igneous Rock Identification
Reference Tables page 6 Scheme for Igneous Rock Identification Determining the properties of an igneous rock then identifying it.
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HOLD ON A SECOND… What is the definition of texture when we are talking about rocks?
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Grain Size
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Non vesicular = No bubbles
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Bubbles
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The mineral crystal size
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Where the rock formed Exited Earth
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Where the rock formed Inside Earth
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Lets see what these words mean.
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Contains magnesium & () () colored Dark colored
Contains aluminum Contains magnesium & () () colored Dark colored Typical continental rock composition Typical () rock composition
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Practice identifying igneous rocks #1
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Lets try to identify an unknown igneous rock
Use the E.S.R.T. Lets try to identify an unknown igneous rock Observed properties of the unknown rock: 1. Light colored 2. Low Density 3. Fine Grained 4. Non vesicular (No gas bubbles)
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4. Non Vesicular (Nogas bubbles)
1. Light colored 3. Fine Grained 2. Low density
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All the rock names are located in this area
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We need to use texture to narrow it down further
Now we have to see where all our known properties meet in the rock name area The rock could be any in the highlighted area, according to color and density We need to use texture to narrow it down further
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The texture was fine and non vesicular
The only place these two textures match is right here
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The correct rock is located in the area where all the properties overlap.
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What do we think our mystery rock is?
Yup, It is a sample of Rhyolite, an extrusive igneous rock Identifying any other igneous rock works the same way!!!
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Now lets take our sample of rhyolite and find out what its mineral composition is.
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Here are the mineral composition percentages
If you do not know where in the rock rectangle to go, assume it is right in the (). Middle Here are the mineral composition percentages
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All of this equals 100% of the rock’s mineral composition.
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We now want to find the individual mineral percentages in our sample of rhyolite
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We now want to find the individual mineral percentages in our sample of rhyolite
24% Potassium Feldspar
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We now want to find the individual mineral percentages in our sample of rhyolite
36% Quartz
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We now want to find the individual mineral percentages in our sample of rhyolite
21% Plagioclase Feldspar
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We now want to find the individual mineral percentages in our sample of rhyolite
10% Biotite
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We now want to find the individual mineral percentages in our sample of rhyolite
8% Amphibole
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Now we know the mineral composition of rhyolite is;
25% Potassium Feldspar 38% Quartz 20% Plagioclase Feldspar 9% Biotite 8% Amphibole All the minerals in the rock are accounted for 100%
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Characteristics of Igneous Rocks
1. Tightly () mineral crystals (unless it looks glassy).
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Characteristics of Igneous Rocks
2. Intrusive Rocks, formed () inside Earth, have visible (sometimes very ()) ().
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Characteristics of Igneous Rocks
3. Extrusive rocks, formed () on the () of Earth, will have a () or () texture.
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