- Slides: 61
Rocks of Fire Igneous Rocks
The interior of the Earth is HOT!
“Yo, How hot is it? ”
So hot, that minerals are MELTED!
I said, that minerals are melted. This is called mag-ma.
Liquid hot magma?
Magma Makes Lava Sometimes, magma rises to the upper part of the Earth’s crust to make lava. When this happens, the cooler crust cools the magma upon contact.
Only small amounts of magma reach the surface as lava.
How does igneous rock form? Igneous rocks form when hot, liquid rock, or magma cools and hardens. Magma Molten rock within and under the Earth’s crust
How does igneous rock form? Magma can cool at high temperatures. It can solidify when nearly 1, 000 degrees C. See the graphic below. As temperature decreases Magma begins to cool Mineral crystals start to form Magma cools more Igneous rocks form
How do geologists classify rocks? Geologists use the following to classify igneous rocks: Composition Texture
DEFINTION: Igneous Rocks that form from the cooling and hardening of lava or magma
If magma cools slowly then the rocks form large crystals.
If lava cools rapidly then the rocks form small crystals.
If lava cools very rapidly then the rocks form no crystals.
Would it be safe to say that the slower the cooling, the larger the crystals?
Minerals are classified by their composition. Are igneous rocks classified the same way? Well, that is partially true. Can anyone here explain?
“I will, Sucka!”
First, magma is classified. �FELSIC MAGMA Thick, sticky, slow-moving, silica-rich, and light colored. Contains aluminum (Al) �MAFIC MAGMA Hotter, more fluid, and low amounts of silica Contains magnesium (Mg) and iron (Fe)
Felsic and Mafic FELSIC MAGMA IS LIKE HOT SYRUP. MAFIC MAGMA IS LIKE A BOTTLE OF REALLY HOT SODA.
Texture too! �In addition to the magma type, Igneous rocks have different textures based on WHERE they formed. They are classified as ▪ INTRUSIVE (form under ground; magma) ▪ EXTRUSIVE (form above ground; lava)
Let’s examine some igneous rocks. Granite Basalt Pumice Obsidian
Granite The most common rock on the Earth’s surface Composed of large crystals of feldspar, quartz, hornblende, and mica
Meet Granite. It’s usually white/gray/pink. Yosemite
Uses of Granite
Igneous rocks, like granite, are also used to make road surfaces. The rock is chipped and hot tar is added. And… What is the purpose of adding tar? ▪ The tar helps to slow down weathering from the atmosphere.
Granite Questions Coming Up How fast did magma cool in order to make granite? Does granite have a coarse or fine texture?
Granite must have formed below the Earth’s surface. Why?
If a rock is made from cooling that occurs below the surface, the cooling happens slowly, and therefore, larger crystals result.
If a rock is made from cooling that occurs in air or water above the Earth’s surface, the cooling occurs quickly, and therefore, smaller crystals or no crystals result.
So Classify Granite, Fool!
Granite is Formed underground, making it INTRUSIVE. Light-colored, making it FELSIC.
So how does Granite get to the surface? If forms under ground, but then gets uplifted to the surface. We don’t see it until erosion removes thousands of meters of rock on top of it. It is pretty common in mountains across the country. (continental crust) The Ground is made of Granite.
Basalt and granite are opposites in that basalt’s crystals are smaller, the color darker, and the texture finer. So basalt is Extrusive or intrusive? Felsic or mafic?
Basalt forms from lava. It is the most common rock formed from lava. It makes up the vast majority of the ocean floor. The ocean is salty. The ocean floor is made of basalt. (But basalt is not salty. )
Pumice and Obsidian These are both volcanic rocks. They both cooled extra quickly.
Pumice has many holes made by gases.
Pumice has a very low density.
Obsidian is nicknamed “natural glass. ”
Igneous Intrusions A rock mass that forms when magma cools inside the Earth’s interior. They are sometimes called plutons. So as volcanoes are extrusive, plutons are intrusive formations.
Here are several igneous intrusions.
Borolanite sill (felsic)
Igneous Rocks Are Subdivided Into Two Classes Volcanic (Extrusive) Volcanic igneous rocks form at the earth's surface as lava cools. Plutonic (Intrusive) Plutonic igneous rocks form deep underground where magma cools slowly.
For 1 Sheepon… Name the rock seen here.
For 1 Sheepon… Name the rock seen here.
Why is gabbro coarse-grained with large crystals? For 2 Sheepons…
Red Light Challenge!
Name 4 minerals found in igneous rocks. For 2 Sheepons… Quartz Orthoclase feldspar Plagioclase feldspar Pyroxene Olivine Muscovite mica Biotite mica Amphibole
____ rocks, like (name one), are made from lava, ash, or dust. For 3 Sheepons…
What metallic element is present in felsic rocks? For 3 Sheepons… Hurry up and take the picture!
All or Nothing! What two European countries, which share the same first letter, have multiple volcanoes?
Follow me to a volcanic ash spa!