1. Atoms and Minerals Magnet and Iron and slide
Quartz SiO2 common mineral

2. Minerals: Building blocks of rocks
Definition of a mineral:
Naturally occurring
Inorganic solid
Ordered internal molecular structure
Definite chemical composition
Definition of a rock:
A solid aggregate or mass of minerals

3. Atomic structure Central region called the nucleus Electrons
Consists of protons (positive charges) and neutrons (neutral charges)
Electrons
Negatively charged particles that orbit around the nucleus
Located in discrete energy levels called shells

4. Flattened structure of an atom
# protons (+) equals # electrons (-)
Electrons in shells
Number of outermost electrons determine types of bonding
Argon
Outermost (Valence) shell

5. Some definitions: Atomic number: number of protons in the nucleus
Atomic Mass: total mass of protons and neutrons within an atom’s nucleus
We can see these on a Periodic Table

6. Column shows # electrons in outermost shell
Periodic Table of the Elements
# protons (+) equals # electrons (-)
Electrons in shells
Number of outermost electrons determine types of bonding
Shows atomic number (# protons) and atomic mass (# protons + neutrons).
Column shows # electrons in outermost shell

7. Electrons are in shells.
Octet Rule:
Atoms larger than Hydrogen and Helium need 8 electrons in their outer shell for stability

8. Neutral Atoms have #protons = # electrons
Silicon has 4 electrons in
Its outer shell
Oxygen has
6 electrons in its
valence shell

9. To satisfy the octet rule atoms can gain or lose electrons In that state they are called IONS They can combine with oppositely charged ions to form neutral molecules
Ions
Oxygen, normally 6 valence electrons, wants 2 extra
Silicon, normally 4 valence electrons, would like to be rid of, or share, 4

10. Chemical Bonding 1: Ionic
Formation of a compound by combining two or more atoms
Ionic bonding
Atoms gain or lose outermost (valence) electrons to form ions
Ionic compounds consist of an orderly arrangement of oppositely charged ions
Usually Columns I (alkali metals e.g. Na) and VII (halogens e.g. Cl)

11. Halite small Na+ large Cl-
Halite (NaCl)- An Example of Ionic Bonding
Table Salt
Na+
Cl-
Na+
Cl-
Na+
Cl-
Na+
Na+
Halite small Na+ large Cl-
Crystalline structure of
Internal atomic arrangement is primarily determined by the size of ions involved
NaCl
Small Sodium ions between large Chlorine ions
(a)

12. Covalent bonding – sharing of valence electrons
Cl2 Chlorine gas
Sharing Electrons in Outermost Shell

13. Covalent Bonds in Water
H2O
Water is polar

14. Other Bond Types Metallic bonding Intermolecular bonding
Valence electrons are free to migrate among atoms
Weaker and less common than ionic or covalent bonds
Intermolecular bonding
Hydrogen bonds- charged regions in water attract
Van der Waals bonds- electrons momentarily grouped on same side of nucleus

15. Isotopes Isotopes and radioactive decay
Atomic mass is the total mass of neutrons plus protons in an atom
An isotope is an atom that exhibits variation in its atomic mass, i.e. different numbers of neutrons
Some isotopes have unstable nuclei that emit particles and energy in a process known as radioactive decay.
12C 13C stable 14C radioactive

16. Structure of minerals Polymorphs
Two or more minerals with the same chemical composition but different crystalline structures
Diamond and graphite (both carbon) are good examples of polymorphs
The transformation of one polymorph to another is called a phase change
Example: Graphite in a High Pressure Cell Makes Diamond
Some polymorphs make good PT indicators

17. Diamond and graphite – polymorphs of carbon

18. Physical properties of minerals
Crystal Form
External expression of the orderly internal arrangement of atoms
The mineral garnet often exhibits good crystal form

19. Physical properties of minerals
Luster
Appearance of a mineral in reflected light
Two basic categories
Metallic
Nonmetallic
Terms are used to further describe nonmetallic luster are vitreous (glassy), pearly, silky, earthy (like dirt), adamantine (greasy)

20. Galena PbS displays metallic luster
Valuable ore of Lead

21. Physical properties of minerals
Color
Generally an unreliable diagnostic property to use for mineral identification
Often highly variable for a given mineral due to slight changes in mineral chemistry
Exotic colorations of some minerals produce gemstones
But we use it anyway
Quartz (SiO2) exhibits a variety of colors

22. Physical properties of minerals
Streak
Streak
Color of a mineral in its powdered form
Helpful in distinguishing different minerals with similar composition
Hardness
Resistance of a mineral to abrasion or scratching
All minerals are compared to a standard scale called the Mohs scale of hardness

24. Cleavage Tendency to break along planes of weak bonding
Produces flat, shiny surfaces
Described by resulting geometric shapes
Number of planes
Angles between adjacent planes
Micas have perfect cleavage
Biotite
Mica

25. Three directions of perfect cleavage – fluorite, halite, and calcite
Each Cleavage Plane is paired

26. Physical properties of minerals
Fracture
Absence of cleavage when a mineral is broken. Shown: conchoidal fracture in Quartz
Specific Gravity
Ratio of the weight of a mineral to the weight of an equal volume of water
Average value is approximately 2.7
Simply hefting a mineral works too.

27. Physical properties of minerals
Other properties
Magnetism
Reaction to hydrochloric acid
Malleability
Double refraction
Taste
Smell
Elasticity

28. Is it calcite or dolomite?

29. Classification of Minerals
Nearly 4000 minerals have been identified on Earth (We discuss a few)
Rock-forming minerals
Common minerals that make up most of the rocks of Earth’s crust
Only a few dozen members
Composed mainly of the 8 elements that make up 98% of the continental crust

30. Commonly formed Ion charges often called “oxidation state”
Metals can form more than one Ion. Fe+2 is name Ferrous, Fe+3 is named Ferric

31. Classification of Minerals
Silicates
Most important mineral group
Comprise most of the rock-forming minerals
Very abundant due to large amounts of silicon and oxygen in Earth’s crust
Basic building block is the silicon-oxygen tetrahedron molecule
Four oxygen ions surrounding a much smaller silicon ion

32. The Component Atoms Silicon has 4 electrons in Oxygen has
Its outer shell
Oxygen has
6 electrons in its
valence shell

33. Remember: atoms can gain or lose electrons They then combine with oppositely charged ions to form neutral molecules
Ions
Anion (negative)
Cation (positive)

34. Silicate Molecule The Silicon-Oxygen O2 - Tetrahedron Si4+ O2 - O2 -
2_25
O2 -
Si4+
O2 -
O2 -
The basis of most rock-forming minerals, charge - 4
O2 -

35. Silicate Bonding I
Oxygen O atoms may obtain electrons from Si atoms, producing the SiO4 -4 Ion.
The negative charge is balanced by positive metal ions.
This occurs in Olivine, (Fe,Mg)2SiO4, a high temperature Fe-Mg silicate. Forms of this mineral are stable 100’s of kilometers below Earth’s surface.
Sort of Ionic Bond

36. Example OLIVINE Fe and Mg Positive ion SiO4 -4 Ion Tetrahedron
facing down
facing up
Positive ion
SiO4 -4 Ion
Independent tetrahedra

37. Silicate Bonding II
Alternately, the oxygen atoms may complete their outer electron shells by sharing electrons with two Silicon atoms
in nearby silicon tetrahedra.
A sort of covalent bond

38. Single chains weakly paired
A Pyroxene
Single chains weakly paired

39. An Amphibole Cleavages 56 and 124 deg Positive ion Double chains (c)

40. Example: Mica
Sheet silicates
(d)

41. Clay Minerals (at high magnification)
note sheet structure
Very small crystals
Kaolinite (hand specimen)
Clays are also Sheet Silicates, just as Micas are
Vietnam Anecdote

42. Framework silicates (e)
Example: Quartz
SiO2
2_26e
Framework silicates
(e)
(3-D, also the Feldspars)

43. Classification of Minerals
Common Silicate minerals
Feldspar Group
Most common mineral group
two directions of perfect cleavage at 90 degrees
In Feldspars, some of the Silicon atoms (oxidation state +4) are replaced by Aluminum (oxidation state +3)
Ion is not symmetrical
Pearly Luster
A Potassium Feldspar

44. Feldspars that use Calcium (Ca) or Sodium (Na) metals to balance
the SiO4 - 4 and AlO4 -5 charges are called:
Plagioclase feldspar
Note the Twinning, seems to have ‘stripes’

45. Summary