Transcript Earth Materials

Earth Materials
Igneous Rocks
I. Rocks are aggregates (mixtures) of minerals or
simply large samples of one mineral.
1. Usually, rocks are polymineralic (have more
than one mineral), such as granite.
2. Rocks are NOT identified using the tests you
used for mineral identification.
3. The minerals in rock help determine the
name of the rock.
4. The origin of the rock determines which TYPE
of rock it is.
II. There are 3 main categories (types) of rocks:
• Igneous: (‘fire’ rock)
• Metamorphic: (have ‘changed form’)
• Sedimentary:(from particles of other rocks)
III. Igneous Rocks
1. Igneous rocks are called ‘fire rocks’ because
they form from lava (surface) or magma
(below ground).
2. Magma is called ‘mineral soup’: the elements come
together that will form minerals as magma cools.
3. Igneous rocks are called the “parent rock”
of all others.
4. All igneous rocks have intergrown crystals,
because they form as the magma cools.
_each crystal grows into the ones around them.
Some crystals are too small to see.
5. Igneous rocks are classified (see page 6 of ESRT)
according to:
a. the mineral composition of the rock, which is
determined by the magma or lava that forms
the rock.
The different colors aid in identifying the type of
igneous rock.
b. The texture, or grain size, of the rock is used to
determine the environment of formation.
This is how quickly or slowly the magma cools to form
rock.
c. Together, mineral composition and texture
identify the rock.
• See page 6 ESRT
• In the Bowen Reaction series, the melting
points for common igneous minerals are
shown. Minerals with high melting points
form crystals first, while those with low (cool)
melting points (typical of crust closer to the
surface) forms crystals last.
6. Environment of formation and crystal size
a. When the magma cools deep below the
ground, it is called intrusive or plutonic, and
the minerals formed will be coarse-grained.
b. When the magma cools NEAR the surface,
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 at the surface and so quickly
no visible minerals form. Vesicular minerals have gas
pockets from gas exploding out.
7. Mineral Composition
Three main igneous families have different
minerals from the lava or magma from which
they formed. (note colors)
a. The basalt family, formed from mafic magma,
makes up the ocean crust. Dark rocks.
• Its density explains why the oceans form
basins. (this crust pushes deeper into earth)
b. The granite family, formed from felsic magma,
makes up the contintental crust.
Light in color.
• This crust is low density (2.7 g/cm3) compared
with the ocean crust (3.0g/cm3).
c. The third family is the diorite family, from magma
that is a mixture of both mafic and felsic minerals.
These are ‘salt and pepper’ rocks and formed at
margins between ocean and continent.
There are also ‘ultra-mafic’ rocks from
deep in the mantle.
• These don’t last too long at surface.
8. In summation, Igneous rocks are identified in
the lab by comparing their:
• composition, which tells you what minerals
are in it, and therefore what magma it came
from, and;
• the texture, which indicates whether the rock
cooled quickly or slowly (extrusive or
intrusive).