Transcript Igneous Rock - Nebulous Zone

Igneous Rock
How Are Igneous Rocks
Classified?
 Igneous
rocks are classified
according to
composition & texture
Composition
 the
minerals of which the rock is
formed.
 Felsic
– light-colored, high silica, low iron
minerals.
 Mafic
– dark-colored, low silica, high iron &
magnesium minerals
What’s the Composition?
mafic
felsic
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.
Name That Texture!
porphrytic
Fine-grained
Coarse-grained
Glassy;
Glassy;frothy;
smooth
vesicular
Types of Igneous Rock

Extrusive 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 preexisting rock and hardens. (underground)
– Also known as plutonic rock.
– Slow cooling
– Coarse-grained texture
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”
Name That Rock!
intrusive
extrusive extrusive extrusive
Igneous
Rocks
Coarse
grained
Fine
grained
Felsic
granite
rhyolite obsidian
pumice
Mafic
gabbro
basalt
scoria
Glassy/
smooth
basalt
glass
Glassy/
frothy
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