Download 6.4 Metamorphic Rock

6.4
Metamorphic Rock
Formation of Metamorphic Rocks
• Metamorphism~ process by which heat,
pressure, or chemical processes change one type
of rock to another
• Formed from existing rock
• Type of rock that forms can indicate the
conditions that were in place at the time of
change
• Two types:
1. Contact
2. Regional
Contact Metamorphism
• ~Change in the texture, structure, or chemical
composition of rock due to contact with
magma
Regional Metamorphism
• ~change in rock due to
changes in temperature
and pressure over a
large area, generally as
a result of tectonic
forces
Classification of Metamorphic Rocks
• Classified by chemical composition and
texture (foliated or nonfoliated)
Foliated Rocks
• ~texture in which mineral grains are arranged in
planes or bands
• Forms in two ways:
1. Extreme pressure may cause minerals to realign
or regrow to form parallel bands
2. Occurs as minerals that have different
compositions separate to produce a series of
alternating dark and light bands
• Example: shale to slate, slate to schist, gabbro to
gneiss (parent rock listed first, metamorphic
second)
Nonfoliated Rocks
• ~mineral grains are not arranged in planes or
bands
• Share one of two characteristics:
1. Original rock may contain grains of only one
mineral
2. Original rock may contain grains that are
round or square
• Examples: sandstone to quartzite, limestone
to marble