ROCK-n-ROLL
• rocks are primarily composed
of minerals
• the oldest are 3.5-4.0 billion
years old
• rocks originated from molten
material (lava or magma)
• Rock Cycle: how rocks change
over long periods of time
IGNEOUS ROCK
• most abundant
• 2 categories
• intrusive - magma cools slowly,
mineral crystals grow large
(course-grained)
• extrusive - lava cools quickly,
minerals form small crystals (finegrained, too small to be seen)
• glasses - sub-category of
extrusive, cool so fast that no
crystals form (ex: obsidian and
pumice)
SEDIMENTARY ROCK
• 75% of the surface rocks
• 3 categories
• clastic - “broken” bits of rock
• chemical - precipitates that
harden out of solution
• organic - sea shells, decaying
plants (limestone, coal)
• fossils almost only found in
sedimentary rock
METAMORPHIC ROCK
• minerals recrystallize due to heat
and pressure
• regional metamorphism - mountain
building
• contact metamorphism - magma is
squeezed through preexisting rock
• 2 categories:
• foliated - layers or bands are
visible
• non-foliated - no layering or
banding