Transcript igneous_rocks

II. Igneous Rocks
Mr. Mathews’ Earth Science 6th Grade
A. Characteristics of Igneous
Rock
• Igneous rocks are classified according
to their origin (where they formed),
texture (how they feel in terms of grain
size, shape, and pattern), and mineral
composition (the minerals that make up
the rock).
1. Origin (where they form)
a. Extrusive Rock
-forms from lava that has exited the
volcano or earth’s crust
Example: Basalt – most common
extrusive, forms most of crust
beneath ocean floor.
1. Origin (where they form)
cont…
• Intrusive Rock
- forms when magma cools and
hardens beneath Earth’s surface.
Example: Granite – most abundant
intrusive, forms most of continental
crust.
2. Texture (how rock feels)
a. depends on size and shape of
crystals/grains
b. The faster the lava cools, the smaller the
crystals
c. The slower the magma cools, the larger the
crystals.
d. Porphyritic texture – rocks with large
crystals AND small crystals
Porphyritic Texture
Porphyritic Texture kind of
like fruit in jello.
3. Mineral Composition
a. Most minerals that make up rock
have silica in them
b. lava low in silica forms dark colored
rocks like basalt
c. magma high in silica forms light
colored rocks like granite.
B. Uses of Igneous Rocks
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Obsidian used to be used to make
sharp tools
Granite used for statues, bridges,
buildings, and decoration
Basalt used to make gravel
Pumice used for cleaning and
polishing