1. 2.1 Geology 8th Grade
Earth Materials: Minerals

2. 2.1. Minerals & Prelude to Rock Groups
Chemical bonding: Focus on covalent bonds
Mineral polymorphs
Physical properties of minerals
Common rock-forming “silicate” minerals
Introduction to rocks & the rock cycle
Volcano building Contest

3. Example: Table Salt: Sodium (Na) and Chlorine (Cl)
Atomic Bonding
Ionic Bonding Review
Example: Table Salt: Sodium (Na) and Chlorine (Cl)
Sodium gives up an electron becoming
a positively-charged charged cation.
Chlorine picks up an electron
becoming a negatively charged
anion.
Bonding between sodium and chlorine in halite
is based on these charge differences.

4. Sharing Electrons: Covalent Bonding Review
Nucleus
Shared electrons

5. Factors that determine the internal structure of minerals:
1) Composition of magma or fluids from which the
minerals form.
2) Conditions under which the mineral forms:
Temperature
Pressure
Minerals comprised of the same elements in the
same proportions can possess markedly
different internal structures.
For example:
Higher pressure -> Denser packing of atoms -> Different mineral

6. Mineral Structure & Conditions of Formation
Different minerals w/ same chemical composition ,
but differing structures, are called “polymorphs”
Graphite (a form of pure carbon)
Soft gray material, e.g., pencil lead
Crystal structure: sheets of carbon
Diamond (also pure carbon)
Forms deep in Earth at high pressures,
& is hardest substance known to humans
Crystal structure: dense & compact

7. Identifying Minerals
- To identify minerals, we use their physical and optical properties.
- Some properties are more diagnostic than others.
- Try to use a combination when making a determination. Useful properties include:
Color
Luster
Hardness
Streak
Crystal form
Cleavage
Fracture
Reaction to acid
Taste
Smell
Magnetization
Elasticity
Specific gravity

8. Physical properties of minerals
Color
Obvious, but often misleading. Slight impurities in a mineral
can change its color.
Example: Quartz (when pure it is colorless), but there are many color varieties which result from small amounts of other elements.

9. Physical properties of minerals
Luster
The appearance of light reflected from minerals.
Examples:
Metallic luster vs. nonmetallic luster
Glassy (vitreous) luster
Resinous luster

11. Physical properties of minerals
Hardness
Very useful! Measures a mineral’s resistance to scratching. We use Moh’s hardness scale (below) for comparisons.

12. Crystal Form Reflects the Internal Arrangement of Atoms

13. Crystal form in halite
(salt; NaCl) is cubic

14. Constancy of angles between crystal faces
A law of mineralogy:
Constancy of angles between crystal faces

15. Quartz (SiO2) The shape of a well-formed crystal reflects
Crystal Form
The shape of a well-formed crystal reflects
directly the orderly internal arrangement of
Its constituent atoms.
Well-formed crystals that grow without
interference are called “euhedral”.
Quartz
(SiO2)

16. Euhedral crystals of quartz

17. Anhedral crystals form when crystals don’t have room
to grow and bump into each other
feldspar in an igneous rock
Irregular boundaries between crystals
due to interference during growth

18. Anhedral crystals
formed by crowding
during growth
Quartz geode

19. Crystal terminations of Anhedral quartz crystals
euhedral quartz
Anhedral quartz crystals
formed by crowding
during growth

20. Euhedral crystals of amphibole in a volcanic rock

21. Cleavage: Tendency to break along preferred planes of weakness.
Cleavages represent directions of
weaker bonding between atoms.

22. 2-directional cleavage in mica

23. In mica, atoms are arranged in weakly-connected sheets

24. Cleaves into long flexible fibers
Asbestos
Cleaves into long flexible fibers

25. Asbestos
Asbestos
group of silicate minerals that readily separate into fibers
that are: thin, flexible, heat resistant, chemically inert
=> many uses
- mainly three types:
chrysotile (“white asbestos”)
crocidolite (“blue asbestos”)
amosite (“brown asbestos”)

27. 3-directional cleavage
Cleavage in both Halite
(salt) & calcite (lime)
is in three directions.
But the angles between
cleavages are different
for these minerals.
Halite has a cubic
cleavage.
Calcite cleaves into
rhombohedra.
Can you spot which is
which in the samples
to the left?

28. In Summary…. Calcite Mica (sheets) Cleavage: Halite
The tendency of a mineral to break along planes of weak bonding in the crystal structure. The number and angles between cleavgae faces are very useful properties for identification.
Calcite
(rhombs)
Halite
(cubes)
Mica (sheets)

29. Conchoidal Fracture in Quartz
Bond strengths
are equal in all
directions.
No preferred
directions of
weakness.
Quartz does not
cleave, but breaks
along smooth,
curved, glassy
surfaces.
Called
“conchoidal”
(glassy)
fracture

30. Conchoidal fracture
in volcanic glass

31. Streak: Color of mineral
in its powdered form
Hematite: Iron oxide

32. “The Acid Test” Carbonate minerals, like calcite, dissolve
in acid and release carbon dioxide
“The Acid Test”
CO2 bubbles

33. Halides Sulfates Oxides Halite (Na, Cl: NaCl) -> common table salt
Important Non-silicate Minerals
Halides
Halite (Na, Cl: NaCl)
-> common table salt
Sulfates
Gypsum (Ca,S,O,H: CaSO4-H2O)
-> calcium sulfate + water, main ingredient of
plaster & other building materials
Oxides
Hematite (Fe, O: Fe2O3)
-> steel

34. Carbonates Calcite (Ca, C, O: CaCO3) Dolomite (Ca, Mg,C, O: CaMg(CO3)2
Important Non-silicate Minerals
Carbonates
Calcite (Ca, C, O: CaCO3)
Dolomite (Ca, Mg,C, O: CaMg(CO3)2
 Found together in sedimentary rock limestone.
 Main ingredient to cement, roads & building stones.

35. The Common Rock-forming Minerals
Over 4000 minerals: only few dozen are abundant, making up most rocks of Earth’s crust
=> rock-forming minerals
Only 8 elements make up most of crust’s minerals & represent over 98% of the continental crust
The two most abundant elements:
Silicon (Si)
Oxygen (O)

36. Average composition of the Earth’s crust.
Question: What minerals would
you expect to be most abundant on Earth?
Percent of elements by WEIGHT
Average composition of the Earth’s crust.

37. The Common Rock-forming Minerals
Earth’s Crust
Primarily Si & O followed in abundance by
Fe, Mg, Ca, Na, K, etc.
Dark colored (mantle and oceanic crust)
Olivine (Si, O, Fe, Mg)
Pyroxene (Si, O, Fe, Mg, Ca)
Amphibole (Si, O, Fe, Mg)
Light colored (crust, esp. continental crust)
Quartz (SiO2) - Hard, transparent
Feldspar (Si, O, Al, K, Na, Ca) - Hard, white, gray, pink
Clay (Mostly come from weathering feldspar)
Calcite (CaCO3, shells) Limestone - Used for cement

38. SiO Basic Building Block of Silicate Minerals:
The Silicon-Oxygen Tetrahedron
An anion with charge of -4
1 silicon (Si) atom
4 oxygen (O) atoms Si 4+ O 2-
SiO 4 4-
Silicon tetrahedron has
An overall charge of -4

39. The Silicon-Oxygen Tetrahedron
Silicates: The Common Rock-forming Minerals
Basic Building Block:
The Silicon-Oxygen Tetrahedron
Tetrahedra link up by forming
covalent bonds between oxygen atoms:
Two tetrahedra can join
by sharing an electron
between adjacent oxygen
atoms
Single silicon tetrahedron:
A silicon atom covalently-
bonded to four oxygens.
Oxygen atom
Silicon atom

41. Double chains: Amphibole Single chains: Pyroxene
The Common rock-forming minerals
Silicates
Silicon-oxygen tetrahedra can be arranged into:
Double chains: Amphibole
Sheets: Micas
Single chains: Pyroxene

42. Balancing Charges in Silicates: Role of Metal Cations
Silicate chains and sheets
Not electrically neutral!
Unsatisfied negative charges of oxygens
located at the edges of chains, or between sheets are
neutralized by coordinating
metallic ions at those sites.
Iron (Fe)
Magnesium (Mg)
Potassium (K)
Sodium (Na)
Aluminum (Al)
Calcium (Ca)

43. Ionic Substitution
Ions of similar size (ionic radius) and charge can substitute for one another in a mineral.

44. 1) Comprised of one or more minerals
Prelude Chapter: Rocks
Definition of a rock:
A rock is:
1) Comprised of one or more minerals
2) Naturally occurring
There are three types of rocks:
Igneous (formed by cooling from magma)
Sedimentary (formed by the breakdown of other rocks)
Metamorphic (formed when preexisting rocks
are heated under pressure.

45. Prelude Chapter: Rocks

46. Prelude Chapter: Rocks
collection of
one or more
minerals
rock

47. Prelude Chapter: Rocks
minerals
rock
mineral

48. minerals rock mineral minerals collection of one or more A collection
Prelude Chapter: Rocks
So far we have:
minerals
rock
mineral
collection of
one or more
minerals
A collection
of one or more
types of atoms

49. Granite & its constituent minerals:
Prelude Chapter: Rocks
Example:
Granite & its constituent minerals:
Quartz
Amphibole (hornblende)
Feldspar

50. Prelude Chapter: Rocks
Rocks and minerals
Some rocks composed entirely of one mineral
limestone (calcite)
Most rocks have more than one kind of mineral
granite
Some rocks contain non-mineral matter
coal (has organic debris)
obsidian (volcanic glassy rock -> not crystalline)

51. Sedimentary Rocks: types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles (detritus) to settle and accumulate or minerals to precipitate from a solution.
Metamorphic Rocks: is a result of a transformation of a pre-existing rock. The original rock is subjected to very high heat and pressure, which cause obvious physical and/or chemical changes.
Igneous Rocks: is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava.
Sediment and Magma:
In groups of two using the supplied materials design an experiment that demonstrates the five different forms of rock found in the rock cycle.
You must have a written procedure and materials list that is detailed easily repeatable.
An explanation of each step and which part of the rock cycle it is representing.