Igneous rockshttp://www.p12.nysed.gov/osa/reftable/earthscience-rt/esrt2010-engw.pdf
Igneous rocks are called ‘fire rocks’
1.
because they form from lava or magma
2.
Magma is called mineral soup
3.
Igneous rocks are the original parent
rocks of all others.
4.
All igneous rocks have intergrown
crystals, because they form as the magma
cools, and each crystal grows into the ones
around them.
5.
Igneous rocks are classified (see page
6 of ESRT) according to:
a.
the mineral composition of the
rock, from the magma or lava that
forms the rock. As old rock pushes
down into the mantle and melts, it
mixes with magma that is already there,
forming slightly different magma.
Over time, different igneous rocks have
formed. Minerals have different colors,
and these colors help identify the type
of igneous rock.
b.
the textureor grain size of the rock,
which is determined by how quickly or
slowly the magma cools to form rock.
c. Together, mineral composition and
texture identify the rock.
6.
In the Bowen’s reaction series, the
melting points for common igneous
minerals are shown
7.
magma cooling deep below the ground
is called intrusive or plutonic, and the
minerals formed will be coarse-grained.
b. magma NEAR the surface cools much
more quickly, the crystals don’t have much
time to form and the rock is called
extrusive or volcanic,
and the minerals will be fine- grained.
c. Glassy minerals form on or above the
surface
8. 3 families of igneous rocks:
granite, diorite and basaltic are identified
according to the type of magma from which
they form.
a.
The GRANITE family, formed
from felsic magma, makes up the
CONTINENTAL CRUST, which is
low density (_2.7g/cm3_) compared
with the ocean crust (_3 g/cm3_).
b.
The basalt family, formed from
mafic magma, makes up the ocean
crust. Its density explains why the
ocean is a basin.
c.
The third family is the diorite
family, both mafic and felsic minerals,
9.
Porphyritic textures refer to igneous
rocks that have VARIOUS sized minerals,
like a chocolate chip cookie. This happens
when the magma cools in stages.
10. In summation, Igneous rocks are
identified in the lab by comparing their:
color, which tells you what minerals are in
it, and therefore what magma it came from
and the crystal/grain size, which indicates
whether the rock cooled quickly or slowly
(extrusive or intrusive).
Metamorphic Rocks are ‘changed’ rocks
1. They can form from any other rock or
rock type.
2. These form when pre-existing 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.
a. May line up differently (foliation)
b. Develop new crystals
3. 4.
Metamorphic Rocks are formed:
a. Heat: contact metamorphism
magma ‘bakes’ a nearby rock. (at
volcanoes, mid-ocean ridges, igneous
intrusions)
b. Chemically:
At mid-ocean ridges when seawater and
sediments mix with hot gases
c. Pressure: Regional Metamorphism
o At subducting boundaries when rock is
ground and deformed
o When mountains form by tension,
compression
o Overlying sediments exert so much pressure
they change the deep rock
5. Metamorphic rocks are classified
according to:
a. Texture: if foliation or banding are
present, the minerals ‘line up’. For
non-foliated rock, there is no
alignment.
b. Composition of the rock: especially
the non-foliated rocks. Classified by
the minerals (the acid test identifies
marble and hardness shows which is
quartzite).
6. Intense pressure from regional
metamorphism: minerals align at a right
angle to the pressure. This often forms the
foliated texture.
7. The type of foliation is described on
page ________ of the _____________.
8. Mica in the rock indicates regional
metamorphism
9.
Rocks changed by intense heat are
often called contact metamorphic rocks:
they are recrystallized due to the presence
of nearby lava or magma flows, which
partially melt the rock.
10. Contact metamorphic rocks are found
along igneous intrusions where the magma
heats the rock.