Rocks
What Is A Rock?
A
rock is a hard substance composed of
one or more minerals.
 It
may also be made of naturally
occurring substances that don’t
perfectly fit the definition of mineral.
– (ex. Obsidian - volcanic glass)
– (ex. Coal – made from once living
organisms
Types of Rock

Igneous
– formed of cooled magma.

Sedimentary
– formed from particles that have been carried
along and deposited by wind and water, and
then pressed together over time.
– Sediments
 the
particles that are carried and deposited.
 Inorganic sediments- bits of rock.
 Organic sediments - shells, leaves, bones, stems.

Metamorphic
– formed when chemical reactions, tremendous
heat, and/or great pressure change rock into
new rocks.
The Rock Cycle

the continuous
changing of
rocks from one
kind to another
over long
periods of time.
*note the
processes
responsible for
each stage
What is Magma?
Slushy mix of molten rock, gases, &
mineral crystals
 Elements in magma

– oxygen (O) , silicon (Si), aluminum (Al),
iron (Fe), magnesium (Mg), calcium (Ca),
potassium (K), sodium (Na)
– silica (SiO2)
 most
abundant in magma
 has greatest effect on magma
 determines igneous rock composition
 affects melting temperature of rocks
 impacts magma flow
How Does Rock Melt?
 Temperatures
above 800°C needed
 Heat to melt rock comes from
– leftover heat of formation
– radioactive decay of elements
 the
process in which an unstable atomic
nucleus loses energy by emitting radiation
in the form of particles or electromagnetic
waves.
What Factors Can Affect Magma
Formation?

Temperature
– Increases with depth in the earth

Pressure
– Increases with depth in the earth
– As pressure increases, melting point increases

Water content
– Changes melting point of rock
– As water content increases, melting point
decreases

Mineral composition
– Different minerals have different melting points
Bowen’s Reaction Series


relationship between
cooling magma &
mineral formation
Two main branches of
crystallization
– Branch 1

Continuous gradual
change of mineral
composition in the
feldspar group
– Branch 2

Abrupt change in
mineral type in the
iron-magnesium
groups
Magma Types

Felsic:
–
–
–
–

light-colored
high silica content
viscous,
flows slowly
Mafic:
– dark-colored
– low silica content
– high iron & magnesium

Ultramafic:
– low silica
– very high iron & magnesium
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Rocks - Nebulous Zone