Download Igneous rocks - Geo

AIM: IGNIS IS LATIN FOR FIRE
Learning Target: I will be able to compare and contrast intrusive and extrusive igneous
rocks and can demonstrate how the rate of cooling affects an igneous rocks texture.
Developmental Procedures:
Do Now: How are intrusive and extrusive igneous rock alike and differ?
(Inquiry Activity) (DOK level 3) (BT) (Pairs Compare 5 mins)
POSSIBLE ANSWERS
Possible Answer : Similarities might include the color, shape, size, texture, or
composition of the rocks. Differences include color, shape, texture, and mineral make
up, gas pockets, holes, crystal sizes
INTRODUCTION TO IGNEOUS ROCKS
Recall from the discussion of the rock cycle that igneous rocks form when magma or
lava cools and hardens. When the red hot lava cools a dark colored igneous rock
called basalt will form. Our ocean floors are made up of basalt. If this melted
materials had stayed deep in beneath the earth and never reached the surface a
totally different kind of igneous rock would form. Different kinds of igneous rocks form
depending its magma cools under ground or above ground.
FORMATION OF IGNEOUS ROCKS
Igneous rocks form from fiery volcanic eruptions above land and under the sea.
Igneous rock also forms deep beneath Earths surface.
This is Granite and is known as an intrusive igneous rock that forms when magma
cools slowly beneath the Earths surface.
DIFFERENCES
This is Rhyolite and it’s a extrusive igneous rock that forms when lava cools quickly at
the Earths Surface.
Question : What do you think is the physical characteristic differences between the
two types of igneous rocks?
INTRUSIVE IGNEOUS ROCKS
Intrusive Igneous Rocks
+ Rocks that form when magma hardens beneath the Earths surface are called
intrusive igneous rocks. That is because they intrude into the existing rocks. We would
never see these rocks were it not for erosion stripping away the overlying rock.
MINERAL GROWTH
Magma consists mainly of the elements silicon and oxygen plus aluminum, iron ,
calcium, sodium, potassium, and magnesium. Magma also contains some gases
including water vapor. Because magma is less dense then the surrounding rocks it
slowly works its way toward the surface. As the magma rises it begin to cool, allowing
the elements in the magma to combine and form minerals. The mineral grows in size ,
forming a solid mass of interlocking crystals. We can see this in our granite example.
EXTRUSIVE IGNEOUS ROCKS
Extrusive Igneous Rocks
You know when magma reaches the surface we call it lava. The lava is very similar to
magma but in the case of lava when its on the surface the gases escape, into the
atmosphere and or no longer trap or restrained in the magma. + When the lava
hardens the rocks that form are called extrusive igneous rocks.
CLASSIFICATION OF IGNEOUS ROCKS
A quick glance at the two rocks that I had previous shown you all and you can clearly
see that they were different. We discussed how the granite contains large mineral
grains and how the rhyolite contains little mineral crystal grains. + Texture and
composition are two characteristics used to classify igneous rocks.
WHAT IS TEXTURE?
Texture describes the appearance of an rock based on its size, shape, and the
arrangements of its interlocking crystals. (xtals) The composition classes of igneous
rocks are bases on the proportion of light and dark minerals in the rock.
COARSE GRAINED TEXTURE
Coarse Grained Texture
The rate of cooling strongly affects the textures of igneous rocks. If magma cools very
slowly , crystals will grow. Slow cooling allows charged to occur in the atoms or ions. +
Slow cooling results in the formation of large crystals. Igneous rocks with large crystal
exhibit a coarse-grained Texture.
FINE GRAINED TEXTURE
Fine Grained Texture
If cooling of magma or lava occurs rapidly the ions in the melted material lose their
motion and quickly combine thus forming tiny crystals. The rapid cooling of magma or
lava results in rocks with small, interconnected mineral grains. We call this fine
grained textures.
PORPHYRITIC TEXTURE
Porphyritic Texture
A Porphyritic texture is one that contains both small grains and large crystals grains.
The rocks that contain porphyritic textures occur due to experiencing different rates of
cooling.
GLASSY TEXTURE
Glassy Texture
A hand specimen of obsidian (volcanic glass). The cooling occurs so rapidly that no
crystals have time to form. Thus, we have a glass (no ordering like in minerals) and
the rock breaks like glass does, with a conchoidal fracture.
GRANITIC COMPOSITION
Igneous rocks in which the light colored silicate minerals such as quartz and
Feldspars are the main minerals are said to have a granitic composition. In grantitic
composition rocks the darker minerals are biotite mica and amphibole.
Intrusive igneous granitic rocks make up most of the continental crust.
BASALTIC COMPOSITION
Basaltic composition rocks are made mostly of dark-colored silicate
minerals and plagioclase feldspar.
EXIT SLIP
Critical thinking
Contrast basalt and granite in terms of how each forms, the texture of each rock, the
color of each rock, and each rock ‘s composition in term of minerals. Using the chart
below to help you.
Please write in a summary. If you just list you just failed….