Transcript Earth Materials

Earth Materials
Metamorphic rocks
Web addressed for pictures are in the
notes section.
I. Metamorphic Rocks are ‘changed’ rocks
• 1. They can form
from any other rock
or rock type.
• 2. These form
when preexisting rocks
are changed due
to heat and
pressure.
• (If the old rock melts, then it does not become
metamorphic, because melted rock produces magma
and igneous rock).
3. Metamorphic rocks are recrystallized/
altered versions of pre-existing rock.
• The minerals often
just line up
differently, but
intense
metamorphism will
cause new minerals
to form.
II. Metamorphic Rocks are formed from:
• a. Heat: contact
metamorphism
• When magma
‘bakes’ a nearby
rock. (at
volcanoes, midocean ridges,
igneous intrusions)
b. Chemical changes:
At mid-ocean ridges when seawater and
sediments mix with hot gases
c. Pressure: Regional Metamorphism
Occurs in 3 environments:
• At subducting boundaries when rock is
ground and deformed
• When mountains form by tension,
compression
•Overlying sediments exert so much
pressure they change the deep rock
III. The two main groups of metamorphic
rocks are the Foliated and Non-foliated
1. The foliated rocks:
a. Texture: foliation or banding are present.
The minerals ‘line up’. This is seen by
observing the texture of the rock
b. caused by intense pressure from regional
metamorphism
• minerals align at a
perpendicular to the
direction of the
pressure. This often
forms the foliated
texture.
c. Types of foliation in ESRT
• Banding: ribbons of
different minerals
• Mica in the rock
indicates regional
metamorphism
2. Nonfoliated rocks:
a. the composition of the rock is important.
• Ex. Quartzite and
marble Try and
identify the minerals
(the acid test
identifies marble and
hardness shows
which is quartzite).
b. Formed often as contact metamorphic
rocks:
• Rocks changed by intense heat .
• They are recrystallized due to the
presence of nearby lava or magma flows,
which partially melt the rock.
c. are found along igneous intrusions where
the magma heats the rock.
• They PROBABLY do not show foliation.
• Identifying
metamorphic rocks is
pretty tricky, and
requires patience
(and sometimes a
good
stereomicroscope)