1. Building Blocks of Rocks and Economic Resources
Minerals
Building Blocks of Rocks and Economic Resources
GLY Summer 2013
Lecture 4

2. Minerals Minerals are a major building block of most rocks
Their properties determine a good part of the physical behavior of the earth

3. Mineral Definition Naturally occurring Inorganic Crystalline
Naturally occurring - not made by man
Inorganic - not formed by a living organism - Teeth, kidney stones, etc. are not minerals
Crystalline - Composed of atoms arranged in a definite three-dimensional pattern

4. Crystal Structure Examples
Halite (left) is common table salt, or sodium chloride, chemical formula NaCl. The large green spheres represent chloride anions ions, while the yellow spheres represent sodium cations.
Fluorite (right) is CaF2 (calcium difluoride). It is Moh’s scale mineral 4, and often occurs in interesting crystals, with either an octahedral or a cubic shape. As the labels indicate, blue spheres are calcium cations, and green spheres are fluoride anions.
In order for a substance to be crystalline, the atoms must be arranged in a definite pattern. These figures show two common patterns. There are over 3500 known minerals, with many different possible patterns.
Halite Fluorite

5. Formation of Halite

6. Atoms Building blocks of all matter - Electrically neutral
Originally thought to be tiny, indivisible particles, but now known to split under certain conditions
They are also known to be composed of smaller particles
Protons (+1) and neutrons (0) in the nucleus, surrounded by cloud of electrons (-1)
Nucleus is about meters, or 1 fermi unit (Unit was named after the Italian physicist Enrico Fermi, who first split the atom in 1942)
The nucleus is surrounded by an electron cloud, whose size is about meters
Thus the nucleus is about 100,000 times smaller than the entire atom

7. Atomic Terminology The atomic number equals the number of protons.
Thus Hydrogen, with one proton, has atomic number 1, and iron, with twenty-six protons, has atomic number 26.
The atomic weight equals the number of protons plus the number of neutrons.
If an iron atom has 26 protons, and 30 neutrons, it has an atomic weight of 56.

8. Chemical Elements
An element is composed of atoms with the same atomic number
Each element has a unique chemical symbol
Hydrogen consists of all those atoms whose atomic number is one, regardless of the atomic weight.
For Hydrogen, it is H. For iron, Fe (from the old name, ferium).

9. Isotopes
An isotope of an element is an atom with the correct number of protons for that element, plus a fixed number of neutrons
Example: Carbon has three isotopes, each with six protons, and with 6, 7, or 8 neutrons

10. Stable or Radioactive An isotope may be stable or radioactive
Carbon isotopes with 6 or 7 neutrons are stable, while the isotope with 8 neutrons is radioactive

11. Chemical Symbols
Atomic number is shown as a subscript before the element symbol - 1H
The atomic weight is shown as a superscript before the symbol - 56Fe
The atomic number is actually redundant, since the chemical symbol implies the atomic number

12. Examples of Chemical Symbols
Particular isotopes are shown using a superscript in front of the symbol
1H is normal hydrogen, with one proton and no neutrons
2H is deuterium, with one proton and one neutron
3H is tritium, with one proton and two neutrons - it is radioactive

13. Ions Ions are charged particles
Cations: Atoms that lose one or more electrons become positively charged
Anions: Atoms that gain one or more electrons are negatively charges
Ionic charge: Shown by a superscript after the chemical symbol, O2-

14. Use of Isotopes Chemical tracers
Study topics such as:
Pollution
Formation temperature
The path of volcanic emissions, etc
Radioactive isotopes are used in estimating the age of materials

15. Compounds Combination of two or more atoms
Combination is called a molecule
Water H2O
Carbon dioxide CO2
Water is a combination of two hydrogen and one oxygen atoms - H2O - here the subscript after the hydrogen tells us there are two hydrogens

16. Molecules Molecules may consist of just one element
Oxygen in the atmosphere is O2
Molecules may consist of several elements, in various amounts
Example: Plagioclase feldspar, the most common mineral on earth NaAlSi3O8 - one sodium (Na), one aluminum (Al), three silicons (Si), and eight oxygens (O)

17. Chemical Bonds The “glue” that holds materials together
Responsible for the properties of matter
On an atomic scale
At the scale of the earth
When two atoms combine to form a chemical bond, energy is released

18. Types of Bonds Ionic Covalent Metallic Hydrogen Van der Waals
Each type is discussed separately on following slides

19. Ionic Bonds Bonds between a cation and an anion
They occur when a cation donates one or more electrons to an anion
They are strong
Dissolve in water
Halite, or table salt, for example

20. Covalent Bonds Equal sharing of electrons by two atoms
Very strong bonds
Compounds usually not soluble
May create molecules that do not readily combine to form larger particles
Ex. Carbon dioxide is strongly bonded within the molecule, but weakly bonded between molecules, so it is a gas

21. Metallic Bonds Outer electrons are loosely held
Properties: Opaque, may have a metallic luster
Bond strength is moderate
Allows them to move between atoms within the solid
Produces high thermal and electric conductivity

22. Hydrogen Bonds
Secondary bond between oxygen on one water molecule and hydrogen on another
Accounts for high melting and boiling points of water
Allows DNA strands to unzip, and later recombine with another strand in sexual reproduction
Weak bonds - About 10-15% as strong as an ionic bond
Hydrogen bonding in water

23. Van der Waals Bonds Diamond Graphite
Accounts for the formation of liquid Helium at 4 degrees above absolute zero (4K)
Occurs in some minerals –
Graphite, between layers of carbon atoms
Residual, extremely weak bonds form by distortion of electron clouds by the presence of a nearby atom

24. Molecules - as strong as the weakest bonds within themselves
Molecular Properties
Molecules - as strong as the weakest bonds within themselves
The oxygen-oxygen (in 02) bond is relatively weak, so these bonds break easily and oxygen reacts with other substances
The nitrogen-nitrogen (in N2) bond is strong, and nitrogen usually will not react

25. Mineral Properties
Depend on the type and strength of bonds and number of bonds (bond density) within themselves
Minerals will be examined in the laboratory, and most properties will be taught there
Examples of mineral properties: hardness, cleavage

26. Hardness
A mineral’s hardness is measured by the ability of a surface to resist abrasion
Hardness is a directional property, although for most minerals the differences are not observable
Fredrik Mohs developed a scale of hardness, based on 10 mostly common minerals

27. Moh’s Scale of Hardness
Any higher number mineral will scratch any lower number.
Moh’s scale is not linear – the difference in hardness between low numbers is much less than between high numbers

28. Cleavage
When a mineral always or usually breaks along a particular plane, it is said to have a cleavage plane
Minerals may have no cleavage, or up to six planes
Cleavage planes occur where there are weak bonds, or low bond density across a plane
(Examples on next slides)

29. Two-directional Cleavage
Selenite, a variety of the mineral gypsum, shows cleavage in two directions

30. Angle Between Cleavage Planes

31. Three-directional Cleavage
Halite, common table salt, shows three directions of cleavage at right angles

32. Three-directional Cleavage
Calcite shows three directions of cleavage, not at right angles
This specimen also shows the property of double refraction. The single cross on the paper is transmitted as two crosses within the crystal

33. Four Directional Cleavage

34. Crystal and Crystal Faces
A mineral sample in which the internal orderly arrangement of atoms is reflected in the symmetrical orderly arrangement of the external surfaces (crystal faces) of a crystal
Apatite, showing a hexagonal prism -
these are crystal faces, not cleavage
planes

35. Identification of Minerals
Minerals are identified based on their physical and chemical properties
A combination of properties are needed, just as no single line from a fingerprint can identify a person
No single property can identify a mineral. A combination of properties are needed, just as no single line from a fingerprint can identify a person
You will learn more about mineral identification in the laboratory

36. Mineral Classification
Classification is based on anion type
Minerals with the same anions have similar properties, while those with the same cations often do not
Mineralogy, the study of minerals, attempts to classify minerals into groups with similar properties

37. Anions Anions may be a single ion
Ex. Oxygen O2-
Anions are often groups of atoms, with the entire group having a negative charge
Ex. Carbonates are CO32- , one carbon with three oxygens, and the whole group with a minus 2 charge

38. Common Anion Groups Silicates, SiO44- Oxides, O2- Sulfides, S2-
Carbonates, CO32-
Phosphates, PO43-

39. Occurrence of Minerals
Over half of all known minerals are silicates, because oxygen is the most common element on earth, and silicon is the second most common.
Silicates are the most important type of rock-forming minerals, those minerals that make up most of the earth’s rocks
Most silicate minerals contain other elements in addition to silicon and oxygen

40. Silicon Tetrahedron
The SiO44- tetrahedron is the basic building block of silicate minerals

41. Silicate Structures

42. Chemistry of the Continental Crust
Eight elements account for almost all of the earth’s crust
Chart is based on weight percent
Oxygen is the most abundant, and silicon the second, which is why most minerals are silicates

43. Felsic Minerals
Minerals with a lot of aluminum and silicon are light in color, and are called Felsic
Many silicate minerals are subdivided based on their chemistry
Plagioclase feldspar, the most common mineral in the earth’s crust

44. Mafic Minerals
Minerals with more iron and magnesium, and less silicon, are dark in color and are called Mafic (from the first two letters of magnesium and the first letter of ferium)
Augite, a type of pyroxene