1. Igneous Rock

2. How Are Igneous Rocks Classified?
Igneous rocks are classified according to
composition & texture

3. Composition the minerals of which the rock is formed. Felsic Mafic
light-colored, high silica, low iron minerals.
Mafic
dark-colored, low silica, high iron & magnesium minerals

4. What’s the Composition?
mafic
felsic

5. Texture
the size, shape, arrangement and distribution of the minerals that make up the rock.
Glassy
the materials are not organized into crystals.
a. Smooth
b. Vesicular- contain gas bubble holes (aka: porous, frothy)
Fine – grained
Has interlocking mineral crystals.
Crystals are small; need microscope to see them.
Coarse – grained
Interlocking mineral crystals are all approximately the same size.
Crystals are large enough to see with the unaided eye.
Porphyritic
large crystals are scattered on a background of small Crystals.

6. Name That Texture! porphrytic Coarse-grained Fine-grained
Glassy; frothy; vesicular
Glassy; smooth

7. Types of Igneous Rock Extrusive igneous rock Intrusive igneous rock
Is formed of lava ( molten rock that reaches the surface of the earth).
Also known as volcanic rock.
Rapid cooling
Fine-grained & glassy textures
Intrusive igneous rock
Is formed when magma pushes up into pre-existing rock and hardens. (underground)
Also known as plutonic rock.
Slow cooling
Coarse-grained texture

8. Uniformitarianism James Hutton Scottish geologist
Described the formation of the features on Earth
Uniformitarianism – states that the processes acting on Earth’s surface today, are the same processes that have been acting on the surface since Earth’s beginning.
“the present is the key to the past”

9. Name That Rock! Felsic granite rhyolite obsidian pumice Mafic gabbro
Igneous
Rocks
intrusive
Coarse grained
extrusive
Fine
grained
Glassy/
smooth
frothy
Felsic
granite
rhyolite
obsidian
pumice
Mafic
gabbro
basalt
basalt glass
scoria

10. What Are Igneous Rocks Used For?
Throughout history, igneous rocks have been used for:
Building materials
Statues
Fortresses
Paving streets (cobblestones)
Curbs
Countertops
Floors
Tools
Abrasives for cleaning & polishing –pumice
Cutting tools & arrowheads - obsidian