4. Rocks- naturally occurring
combinations of mineral
• 1. Most contain at least 2 minerals.
• 2. A few have only 1
• 3. Only 20 minerals are commonly found in
rocks.
• James Hutton- first to say that rocks formed
from molten materials, not from minerals
crystallized by water as previously thought
• Molten- a solid object formed from liquid
material
5. I. Igneous Rock
• A. Formation of igneous rock
– 1. crystallization- as magma cools below
ground, the movement of ions in the liquid
slows and the ions arrange into solid, more
orderly patterns
– 2. Rate of Cooling-
• A. slow cooling deep in the earth forms very
large crystals.
7. b. Faster cooling
nearer the surface
forms very small
crystals
1. Rocks formed
in this way are
fine-grained and
called
Extrusive
2. examples:
basalt, andesite,
rhyolite
8. C. Instant cooling
would result in
rocks made of
unordered atoms
and no definite
crystal pattern.
1. These are
referred to as
glass.
2. examples:
obsidian, pumice
9. • d. When crystallization occurs in areas with
much water, unusually large crystals may
form.
– 1. These are called pegmatites.
– 2. They often contain valuable minerals and gems
like beryl and topaz.
10. 3. Composition of Magma
• A. silicon, oxygen, aluminum, sodium, potassium,
calcium, iron, and magnesium are the 8 most
common mineral materials.
• B. some materials called volatiles (water vapor,
CO2) also volatiles- materials commonly found as
a gas at surface level temperatures and pressures
c. minerals in magma will crystallize at different
rates and temperatures giving igneous rocks
varied appearances
11. 4. Igneous textures
• A. texture- describes overall appearance of
the rock based on size and arrangement of the
interlocking crystals
• B. Texture can reveal details about the
environment in which the rock formed.
12. • 1. Fine-grained textures (called aphanitic) are
in igneous rocks formed near the surface
– A. individual minerals cannot be identified so
classification is by color-light, intermediate, dark
– B. many can have elongated openings called
vesicles through which gases have escaped
– C. igneous rocks formed with this texture are
called extrusive
13. • 2. coarse-grained textures (called phaneritic)
are in rocks that form deep in the ground
– A. individual minerals can easily be identified due
to the large crystals
– B. igneous rocks formed with this texture are
called intrusive
14. • 3. Some igneous rocks begin to cool deep
below surface, then get brought upward to
finish cooling more quickly
– A. they have some large crystals and some very
small ones
– B. these have porphritic textures, with the large
crystals called phenocyrsts and small ones called
groundmass
15. 4. Glassy textures
• A. form when magma is thrown upward
during eruptions which cool them instantly
• B. example: obsidian- looks like a dark chunk
of man made glass, used in Native American
arrowheads pumice- very light –weight rocks
that have many vesicles and can float on air or
water
21. 2. Sequence descriptions
• A. olivine and pyroxene form first, are rich in
iron and magnesium, and are very dense
• B. igneous rocks that contain these dense
minerals are called mafic rocks and are usually
black or dark green
– 1. they form from magma ~ 900º C (1620º F) -
1200ºC (2160ºF)
– 2. ex: basalt- makes up most of ocean bottom,
gabbro-found on many Pacific Islands
22. • C. igneous rocks that contain low-density
minerals are called felsic and are light colored.
– 1. they form from magma about 800ºC (1440º F)
and contain quartz and feldspar minerals
– 2. ex: andesite, rhyolite, and the most common
rock of all *granite*
23. Uses of Igneous Rock
• 1. Carvings and inscriptions made in granite
can withstand weathering
–Ex. Vietnam Veteran’s Memorial wall in
Washington, D.C.
24. • 2. Pumice is ground up
and used as a scouring
powder
• 3. Some igneous rocks
have valuable minerals
like iron, copper, and
uranium mixed in.
