Download Nonfoliated Rocks

Foliation develops when minerals flatten out or line up in bands.
At low levels of metamorphism, the bands are extremely thin, as in slate.
With higher pressure and temperature, the mineral mica can grow and
make the rock look shiny, as is common in phyllite and schist. At even
higher levels of metamorphism, the minerals in the rock tend to
separate into light and dark bands, like those in gneiss.
How do rocks change as foliation develops?
Nonfoliated Rocks
Metamorphic rocks that do not show foliation are called nonfoliated
rocks. One reason a metamorphic rock may not display foliation is that
it is made up mainly of one type of mineral, so that different minerals
cannot separate and line up in layers. One common nonfoliated metamorphic rock is marble, which develops from limestone. Marble is used
as a decorative stone. It is good for carving and sculpting. Because
marble is nonfoliated, it does not split into layers as an artist is working
with it. Another example of a nonfoliated rock is quartzite. It forms
from sandstone that is made up almost entirely of pieces of quartz.
Another reason that a metamorphic rock may lack foliation is that
it has not been subjected to high pressure. Hornfels is a metamorphic
rock that can form when a rock is subjected to high temperatures.
Hornfels, which often forms when magma or lava touches other rock,
is nonfoliated.
What are two reasons a metamorphic rock might not
show foliation?
KEY CONCEPTS
CRITICAL THINKING
1. What conditions can cause
a sedimentary or igneous
rock to change into a
metamorphic rock?
4. Draw Conclusions Would
gneiss be more likely to form
at shallow depths or at great
depths where mountains are
being pushed up? Why?
2. How do new minerals grow
within existing rocks?
3. Why do bands of minerals
develop in most metamorphic
rocks?
5. Infer Would you expect to
find foliated or nonfoliated
metamorphic rocks next to a
lava flow? Why?
CHALLENGE
6. Synthesize What features of
sedimentary rocks are unlikely
to be found in metamorphic
rocks? What features of metamorphic rocks do not occur in
sedimentary rocks?
Chapter 3: Rocks 101