1. Rocks and Minerals
Text Chapter 7

2. KEY POINTS: ATOMS & ELEMENTS
(AtomsElementsMineralsRocks)
• Rocks are made up of one or more minerals.
• Minerals are composed of one or more
elements.
• Elements such as oxygen or iron are made up
of groups of like atoms.
• Atoms are composed of combinations of
protons, neutrons, and electrons.
• Atoms of elements are joined together by
bonds.

3. Minerals
•Rocks are made up of
one or more minerals.
•Geologists have
identified more than
4,000 different minerals.
•But only about 20
minerals are commonly
found in rocks.
•Typically, individual
rocks are composed of
just a handful of
minerals.
•Granite (R) is composed
of 4:
quartz, feldspar, hornble
nde and biotite (a type
of mica).

4. Most Common • Granite is an igneous rock that is
Elements in composed primarily of four
Granite Minerals minerals. Magma cooling very
•Quartz (oxygen & slowly far under the earth's
silicon). surface, allows crystals of the four
•Feldspar minerals to grow large enough to be
(oxygen, silicon, aluminu easily seen by the naked eye. These
m, calcium, sodium & minerals are
potassium) quartz, feldspar, mica, and usually
•Mica hornblende.
(oxygen, silicon, aluminu
m, iron, calcium, magnes
ium & hydrogen).
•Hornblende [a.k.a.
amphibole]
(oxygen, silicon, aluminu
m, iron, calcium, magnes
ium & hydrogen).

5. Quartz vs.
Hornblende (a.k.a.
amphibole)
The mineral quartz
(top R) is composed of
just two elements:
silicon and oxygen.
Other minerals may
contain many
elements.
Hornblende or
amphibole (bottom R)
is made up of
calcium, magnesium, i
ron, aluminum, silicon,
and oxygen.

6. Four of the Most Common Minerals
• Quartz
quartz is a common mineral that is found in many different types of rocks. The chemical formula
is Silicon oxide (SiO2). Impurities in the rock at the time of formation causes the quartz crystal to
produce different colors. Quartz can be colored yellow, milky white, rose, brown to black, blue
and the best known color purple amethyst.
Feldspar
Feldspar is the most abundant mineral in rocks that are located at or near the earth's surface.
Feldspar can have a glassy white, blue, green, pink or red crystals. When feldspars are exposed to
the atmosphere they weather easily. Clays are formed by weathered feldspar.
Kaolinite is the highest quality of the feldspar clays used by potters.
• Hornblende:
Hornblende is a mineral that contains magnesium, iron, silica and aluminum. Hornblende is
black, brown and green in color. It occurs in crystals of many igneous rocks.
• Mica:
Mica can be clear, black, green, red, yellow, brown, purple lapidolite and other colors too. Clear
mica was named Muscovite because it was found near Moscow, Russia. It was used as window
glass in the Muscovite's homes. Muscovite contains water which helps to make it clear. Biotite
mica is dark green to black in color because it contains metals such as iron and magnesium.

7. What are Minerals
Made of? Elements!
•Minerals can be
categorized by the
chemical elements they
contain.
•There are 92 naturally
occurring elements on
Earth.
•98% of the rocks in the
crust below our feet are
mainly composed of just
8 elements.
•These eight elements are
common ingredients in
everyday objects or in the
foods we eat.

8. Eight Most Common Elements in Continental Crust
(The most common minerals in Earth’s crust are
composed of the most common elements.)

9. Certain elements are
vital for human
health.
•Human food contains
many of the common
elements that are naturally
extracted from rocks as
minerals break down at
Earth’s surface to form soil.
•These elements are
absorbed by crops growing
in soils and find their way
to our bodies via the food
we eat.
•Many of the elements are
essential for good human
health.

10. Elements and Atoms
• Elements can’t be subdivided into other
materials.
• Elements can be separated into individual atoms.
• An atom is the smallest particle that retains the
characteristics of an element.
• Atoms are composed of one or more of the same
three basic components: electrons, neutrons and
protons.
• The number of protons in an atom is unique for
each element and is called the element’s atomic
number, e.g. oxygen = 8; silicon = 14 (protons).

11. Helium Atom (not to scale). Note: charges
of electrons, protons, & neutrons.

12. Helium and Neon: In all atoms electrons lie in energy levels
around the nucleus. There are only 2 electrons in the first
level, and maximum of 8 electrons in the second level. In these
two elements the number of electrons = protons, so they don’t
form ions and don’t bond with other elements.

13. Ions and Bonds
The outer energy levels of
many elements are
incomplete.
These elements may gain
electrons from other
elements or may lose
electrons.
Atoms that lose or gain
electrons are known as
ions and have a positive or
negative electrical charge.
Positive and negative Ions
of individual elements are
attracted to each other
and bond together to form
minerals (note sodium
chloride, R).

14. How salt is formed from two ions
(negatively and positively charged) seeking
stability via an ionic bond.

15. Covalent
Bonding
Water (H20), one of the
most common substances
on the planet is composed
of two atoms of hydrogen
(H) and one of oxygen (O).
Each hydrogen atom has
an electron that is shared
with oxygen to give it a full
energy level.
Likewise, oxygen shares an
electron with each of the
hydrogen atoms.
This type of sharing is
called covalent bonding
and typically occurs where
atoms share electrons to
achieve a stable structure.

16. Together oxygen and silicon account for 70% of the
atoms in the Earth’s continental crust. Many crustal
minerals are mainly combinations of these two
elements.

17. Common Silicate Structures (tetrahedron combinations
that form 1. olivine, 2. pyroxene group, 3. amphibole or
hornblende group, 4. mica group, and 5.
quartz/feldspar group).

18. The Silicates
The bonding of silicon
and oxygen atoms
forms a pyramid-like
shape known as the
silica tetrahedron.
Minerals made of
silicon and oxygen are
known as silicates.
Silicates feature
atomic structures that
are characterized by
different
arrangements of the
silica tetrahedron.

19. Tetrahedra =
Basic Building Blocks
• These basic building blocks, the tetrahedra, can be
joined together in combination with other elements
(using ionic or covalent bonds or both) to form
different silicate minerals such as those found in
granite.
• The amount of silica present in magma is especially
significant in controlling magma viscosity.
• Silica combines with other elements in magma (e.g.
iron, magnesium, potassium).

20. Silica content determines magma
viscosity.
• In magmas with low silica content atoms combine
to form minerals such as olivine and pyroxene
with simple forms like pairs and single chains.
• With more silica, the tetrahedra form complex
double chairs, sheets, and three-dimensional
frameworks.
• These larger, more complex forms get tangled
together in the magma, making flow difficult and
resulting in higher viscosity

22. Bond Strength/Weakness
• Ionic bonds formed by electrical attraction are typically
weaker than covalent bonds where electrons are
shared.
• Minerals composed of ions that form covalent bonds
are typically stronger, and therefore more likely to be
preserved on the Earth’s surface, than those with only
ionic bonds.
• The diamond, the hardest mineral, is formed of carbon
atoms that share covalent bonds among four
neighboring atoms.

23. Character of Rocks
• Rocks’ character depends to a large degree on
the atomic structures of their minerals and the
way the atoms are bonded together.
• Some minerals are strong, like quartz, and appear
in a variety of roles in different rock types.
• Other minerals have weak bonds and will dissolve
in water.
• The combination of elements combining to form
minerals will determine the melting temperature
of rocks and behavior of the magma produced.

24. MINERALS: KEY POINTS
• A mineral is a naturally occurring, inorganic solid with a
definite chemical composition and uniform atomic structural
elements.
• Minerals can be identified on the basis of characteristic
physical properties such as:
(The four features used most often to characterize minerals)
1. Crystal form
2. Cleavage
3. Hardness
4. Color
(The two less common features used)
5. Luster, and
6. Streak

25. Crystal Forms
The shape of a mineral
crystal is related to the
way the chemical
bonds form.
Atoms or molecules of
a mineral align in a
uniform manner to
form a crystal
structure.
Common shapes are
prisms, pyramids, nee
dles, cubes and
sheets.

26. Cleavage
Depending on how
their constituent
atoms are
arranged, minerals
may brake along
specific surfaces of
weakness called
cleavage planes.
Cleavage planes mark
those parts of the
mineral where ions
are connected by
relatively weak ionic
bonds.

27. Cleavage Planes
Covalent bonds are
strong and less likely
to form cleavage
planes.
Mica separates into
sheets (R).
Other minerals may
have multiple
cleavage planes:
sheets, cubes or
other shapes.
Quartz has none.

28. Hardness
Ten minerals make up
the Mohs hardness
scale (R).
Minerals not in the
table are ranked
relative to these.
For example, a mineral
that could scratch
feldspar by not quartz
would have a
hardness of about 6.5.
A copper penny ranks
around 3; glass 6.

29. Mohs Hardness Scale

30. Color
Used imperfectly to
describe minerals.
Minerals come in a variety
of colors.
However, some minerals
exist in a wide range of
colors.
Quartz, for
instance, occurs in over a
dozen different colors.
And, minerals can change
color when they are
exposed to changing
natural conditions
(rain, heat) on or near the
Earth’s surface.

31. Luster and
Streak
Luster = how light is
reflected from a mineral.
Streak = the mark
formed when a mineral
is scratched across an
unglazed piece of
porcelain.
Gold creates a yellow
streak; iron sulfide
makes a black streak.
Other properties: calcite
creates bubbles of CO2
when exposed to acids;
and sulfur smells bad.

32. Summary
Flow Chart

33. Three Classifications of Rocks:
Igneous, Sedimentary and Metamorphic
(differentiated on the basis of their chemical and
physical properties)

34. Igneous Rocks: KEY POINTS
• Igneous rocks form from the cooling of melted rock
(magma).
• When magma reaches the surface it cools quickly and
solidifies into small mineral crystals in volcanic igneous
rock.
• If magma solidifies below the surface, it cools slowly to
form large mineral crystals in plutonic igneous rock.
• Igneous rocks can be classified by texture and color
(indicating mineral composition)
• Types of igneous rocks vary with plate tectonic settings.

35. Plutonic vs.
Volcanic Igneous
Rocks
Igneous rock is formed
through the cooling
and solidification of
magma or lava.
Igneous rock may form
either below the
surface from magma
as intrusive (plutonic)
rocks or on the surface
as extrusive (volcanic)
rocks from lava.

37. Igneous landforms: Volcanic process form
volcanoes, lava flows and ash falls. Plutonic
process lead to batholiths, laccoliths, dikes, sills
and crystallized magma chambers called “stock.”
Another Version of
Figure 7.18

38. Batholith:a great mass of intruded igneous rock that for
the most part stopped in its rise a considerable distance below
the surface (Stone Mt. Georgia & its confederate memorial).

39. Half Dome, a granite monolith in
Yosemite National Park is part of the
Sierra Nevada batholith.

40. Laccolith = a mass of igneous rock that is intruded
between sedimentary beds and produces a domical bulging of
the overlying strata

41. Sedimentary Rocks: KEY POINTS
• Clastic sedimentary rocks: composed of sediments –
rock and mineral fragments that form when rocks
break apart at or near Earth’s surface. Clastic
sedimentary rocks make up the majority of all
sedimentary rocks.
• Chemical sedimentary rocks: crystallized from a
solution, e.g. seawater, as a result of changing
conditions.
• Biochemical sedimentary rocks: form by the actions of
living organisms or are composed of the remains of
dead organisms.
• Often form in a series of layers called beds or strata.

42. Clastic Sedimentary Rocks
• Clastic sedimentary rocks are formed from
rock and mineral fragments (clasts).
• This process occurs in a series of steps:
1. Generation of clasts due to the breakdown of
an original rock by weathering;
2. Transportation of the eroded material from
the source area; and
3. Lithification—the deposition and subsequent
conversion of the material to rock.

43. Sedimentary Rocks: Typically are
composed of beds or strata.

45. Limestone (a sedimentary rock deposit) permits
water to seep through it and form caverns.

46. Sedimentary Process

47. Sedimentary Process (Cont’d)

48. Metamorphic Rocks: KEY POINTS
• Metamorphism relates to changes in mineral
composition or texture that occur in solid rocks as a
result of increasing pressure or temperature.
• The temperature range for rock metamorphism is
approx. 200 to 1,100 degrees C (390-2,010 degrees F).
• Contact metamorphism: occur when rocks come in
contact with a heat source (usually magma).
• Regional metamorphism occurs when rocks undergo
increased temperatures and pressure typically
associated with the plate tectonic processes that form
mountains.

49. Igneous Rocks Relative abundance of
in the earth's crust (basalt and gabbro
dominate the igneous category).

50. Metamorphic
Rocks
Relative
abundance of
metamorphic
rocks in the
earth's crust
(gneiss
dominates).

51. The Rock Cycle and Minerals: KEY
POINTS
• The rock cycle links the principal
igneous, sedimentary, and metamorphic rocks
together in an idealized view of the formation
of rocks in the Earth’s crust.
• The rock cycle serves as an example the Earth
operates as a system and constantly changes.
• Minerals form in a range of geologic settings
associated with the formation of the most
common rock types.

52. Sedimentary
Rocks
Relative
abundance of
sedimentary
rocks in the
earth's crust
(shale
dominates).

53. The Rock Cycle

54. The Rock Cycle

56. The Rock Cycle (takes millions upon millions of
years for Louie or Billy to go around just once).