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ROCKS
What is a Rock?
• A group of minerals bound
together
• Naturally occurring solid
 Can consist of mostly one
mineral or
 Several different minerals
in varying quantities
 Rocks are classified
according to the processes
by which they are formed
3 Major Rock Groups
1. Metamorphic – rocks formed
when an existing rock is
transformed by heat, pressure,
or chemical reactions.
• Rock pulled beneath Earth’s
surface; movements in crust
• Rock is heated and undergoes
changes
• Metamorphic change happens
in solid state ; w/o melting
• Pressure changes the way the
particles line up
2. Igneous – rocks formed when
hot, molten rock, or magma,
cools and hardens either
inside Earth or at the surface
• Rock pulled deeper under the
surface, melt at 600 -1300˚ C
• The molten rock called Magma
rises, cools, and solidifies
3. Sedimentary – rocks
formed over time as sediment
is compacted and cemented
together
• Weathering
• Sediment
• Erosion
• Deposition
• Compaction
• Cementation
http://www.youtube.com/watch?v=BpXR-z47G8o
http://www.youtube.com/watch?v=pg_jKJFbA
2A
Igneous Rock
2 Types
I.
Extrusive Igneous Rock
a. Magma explodes out of the
Earth, becomes Lava
b. Lava cools quickly, small
crystals
c. Volcanic rocks
II. Intrusive Igneous Rock
a. Magma cools and hardens
underground as it is pushed
toward surface
b. Slow cooling, large crystals
c. Plutonic rocks
d. Intrusions – masses of rock
that harden with the Earth
How Does Magma Form?
1. Mantle Rock Rising – less
pressure allows for melting
2. Addition of Volatiles – Chemicals
that exist in gasous form and mix
with hot rock to break bonds
3. Heat Transfer – rising rock brings
heat to melt crustal rock
Pyroclastic Debris:
pyro – fire
Clast – broken
•Fine particles of glass or
volcanic ash that form as a spray
of lava erupts into air and
quickly cools
•Or large bombs erupted as liquid
and cooled
Identifying Igneous Rocks
a) Grain size
i.
Coarse – large enough to
identify
ii. Medium – can see grains
but can’t identify
iii. Fine – too small to be seen
iv. Glassy – no grains at all
b) Texture- arrangement of grains
i. Crystalline – interlocking
grains
ii. Fragmental – Chunks or
large pieces cemented together
iii. Glassy – shiny, no grains
iv. Porous – sponge - like
c) Composition – proportions of
chemicals/minerals that make up
the rock
i. Felsic – rich in silica (silicon
& oxygen), light colored
ii. Mafic – poor in silica, dark
colored
iii. Ultramafic – very low silica
iv. Intermediate – in between