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Chapter 9
Rocks and Minerals
The Study of Minerals
Minerals are the building blocks of rocks…
Minerals include compounds like quartz,
iron, and halite…
Composition of Minerals
• Minerals are not mixtures…
• Minerals are elements or compounds with
definite chemical compositions and
properties.
• Only some minerals are found in the
earth’s crust as pure substances…
• An example would be gold, sulfur, and
diamonds.
Composition of Minerals
• The most common element in mineral
compounds is oxygen – about 47% of
earth’s crust.
• Silicon is the next most abundant – 28%
• And aluminum is the third – 8%
Minerals
• Minerals can also be found dissolved in
water…
Minerals
• Minerals are classified by chemical
composition into several groups:
1. Native elements (The smallest group):
naturally occurring, uncombined
elements – gold, sulfur, carbon, and
arsenic.
Minerals
2. Halides:
fluorine, chlorine, bromine
halite (NaCl)
only a handful of halides are common
in the crust
Minerals
3. Sulfides
this group contains sulfur
pyrite – fool’s gold
cinnabar (HgS)
4. Oxides
contain the element oxygen bonded to a metal
5. Carbonates
contain the carbonite ion (CO3)
calcite
6. Silicates
The largest group
contain the elements silicon and oxygen
Quartz
Structure of Minerals
• A characteristic of minerals is that they all form
crystals.
• Crystals are geometric shapes composed of
atoms or molecules arranged in repeating threedimensional patterns.
• They are identified based on the number of flat
surfaces or “faces” that they have.
• Types of minerals share the same characteristic
shape.
• Some minerals may be formed in different ways
forming different crystals – like carbon
Structure of Minerals
• Isometric
three equal axes
at right angles to each
other…
• Ex: galena
Structure of Minerals
• Tetragonal
three axes at right
angles, but one is
longer than the other
two
• Ex: zircon
Structure of Minerals
• Orthorhombic
three unequal
axes at right angles to
each other
• Ex: sulfur
Structure of Minerals
• Monoclinic
three unequal
axes, two at right
angles and the third
at some other angle
with the two.
• Ex: gypsum
Structure of Minerals
• Triclinic
three unequal
axes, none at right
angles with the
others.
• Ex: amazonstone
Structure of Minerals
• Hexagonal
three equal axes
at 120 degrees
angles and a forth
longer than the others
at right angles to
them.
• Ex: quartz
Classification of Rocks
There are three rock classifications:
1. Igneous rocks
from molten rock
2. Sedimentary rocks
from sediments
3. Metamorphic rock
from alteration of rocks by heat and
pressure
Igneous Rocks
• Igneous rocks have a fiery formation
• They are formed from magma and lava
when it solidifies
• Igneous rock formed and cooled under
ground is intrusive rock (or plutonic)
• Igneous rock formed and cooled above the
surface is extrusive rock (or volcanic)
Igneous Rock
• Igneous rocks are
classified by their
texture…
• Coarse-grained
igneous rocks
• have larger crystals
• they are formed
intrusively
• the most common is
granite
Igneous Rock
• Fine-grained igneous
rock
• formed quickly
• these are formed
extrusively during a
volcanic eruption
• an example is rhyolite –
which has the same
composition as granite
• the most abundant
extrusive rock is basalt
Igneous Rock
• Mixed texture igneous rocks
• Smooth-textured igneous rocks
these cool very quickly
ex: obsidian
• Porous Rocks
these contained dissolved gases
the gases left holes in the rock
ex: pumice
• Scoria
known as volcanic slag
formed like pumice but is denser
Sedimentary Rocks
• Most of the earth is
covered in a thick
layer of sediments…
• Sediments are
deposits of mineral
fragments (usually
laid down by water)
• Most sediment has
been fused together
by heat, pressure,
and chemical action…
Sedimentary Rocks
Mechanical Sediments:
Laid down by forces of nature –
flood, wind, etc…
It is then “glued” together by
pressure
This sediment is called clastic
sedimentary rock
Sedimentary Rock
Examples:
Sandstone – may contain fossils
Shale – most common sedimentary
rock – is easily split into slabs
Conglomerate Rock – contains rough
fragments known as breccia.
Metamorphic Rock
• Metamorphism changes rock into new rock.
• They have specific characteristics –
– They show evidence of having been under great
pressure
– For example: quartz is harder and denser than
sandstone
– They also reveal evidence that changes were brought
about by heat and chemicals
– For example: some of these rock show more crystals
– Some minerals not ordinarily found in other rocks are
seen in these after metamorphism.
Metamorphic Rock
Two basic types of
metamorphic rock:
1. Foliated rock
layered rock
example: slate
Metamorphic Rock
2. Unfoliated
unlayered
example: marble
formed from
limestone