Igneous Rocks Review and Practice

Pg 6,
ESRT

Extrusive Igneous Rocks

Intrusive Igneous Rocks

Formed as LAVA erupts from
volcanoes on Earth’s surface

AKA Volcanic environment of
formation

Cools quickly! (seconds to hours)

Formed as MAGMA intrudes into
Earth’s crust from the mantle

AKA Plutonic environment of
formation

Cools slowly! (days to millions of
years)

●Fine-grained (crystals too
small to see without
magnifying)

●Glassy texture

●Vesicular (air pockets/gas
bubbles)

●Coarse-grained (crystals
easy to see without
magnifying)

Characteristics

Formation

Extrusive Igneous Rocks

Intrusive Igneous Rocks

Vesicles (air bubbles/gas
pockets)

Glassy

Fine-grained

Coarse-grained
- crystals big
enough to see
without a
magnifying
glass!

Extrusive
rocks

Intrusive
rocks

Felsic rocks
(light color, low
density)

Mafic rocks
(dark color,
high density)

Estimating
percentages of
minerals within
igneous rocks.

1. Draw a line through
the rock name straight
down (vertically)
through the mineral
composition chart.

2. Estimate the
relative percentages
of each mineral using
the scale on the side.

3. Make sure that you
percentages total up
to 100!

35% potassium
feldspar
(100-65=35%)

38% quartz
(65-27=38%)

15% plagioclase
(27-12=10%)
7% biotite
5% amphibole

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