Transcript Metamorphic Rocks - Tapp Middle School

Metamorphic Rocks
Ch 4 S4
Introduction

Rocks can go through process of
metamorphism
– Metamorphism: a change in the constitution of
rock; specifically : a pronounced change
effected by pressure, heat, and water that
results in a more compact and more highly
crystalline condition
Metamorphic rocks are rocks in which the
structure, texture, or composition has
been changed
 Can be changed by heat, pressure, or
both

Origins of Metamorphic Rock
 Texture/mineral
composition can
change (∆) when surroundings
change (∆)
 Occurs between 50ºC & 1,000ºC
– Can occur over 1000ºC
 Metamorphic
change takes place
more than 2 km beneath the surface
of the Earth
Contact Metamorphism
– Occurs near igneous intrusions
– Occurs near bodies of magma
– Rock is heated and changed by the
nearby magma
Regional Metamorphism
– Occurs when pressure builds up in rock
buried under other rock formations or
when Earth’s crust collides
– Occurs over thousands of km3 within the
rocks crust
– Found beneath continental rock
formations
Regional & Contact Metamorphism
Composition of Metamorphic Rock
Metamorphism occurs when temperature
& pressure inside the Earth’s crust change
 Minerals change into different minerals
that are more stable in the new
environment
 Index minerals: minerals that form only at
certain temperatures & pressures

– Used to measure temperature, depth, &
pressure at which a rock undergoes
metamorphosis
– Include: biotite mica, chlorite, and garnet
Recrystallization & Index Minerals
Textures of Metamorphic Rock
2
textures
– Foliated
– Nonfoliated
Foliated Metamorphic Rock
Texture: mineral
grains are
arranged in planes
or bands
 Contains aligned
grains of flat
minerals
 Diagram shows a
sedimentary rock
transforming via
metamorphism

Nonfoliated Metamorphic Rock
Texture: mineral
grains are not
arranged in planes
or bands
 Made of one or
only a few minerals
 Mineral crystals
may change in size
or mineral may
change in
composition

Metamorphic Rock Structures

Deformation: a
change in the
shape of a rock
due to a force
placed on it
– Rock may be
squeezed or
stretched
– Bends in the rock
are indicators