MINERALS
Basic Chemistry
Physical Properties
What’s Important
• Basic Chemistry
– Atom, ion, cation, anion, proton, neutron, electron, isotope
– Bonding—ionic, covalent, metallic, van der waals
• What is a mineral?
• What properties are characteristic of each mineral?
• What causes those properties?
• Dirty Dozen—12 important minerals
• A rock is an aggregate of minerals
Basic Chemistry
• 106+ chemical elements
• Compounds are made up of elements
• Atom
– Smallest particle of matter that still retains the properties of the
substance
– Size is measured in Angstroms = 10-10 m or 10-8 cm
– Mass measured in Atomic Mass Units (AMU)
• 1/12 the mass of a carbon atom
Basic Chemistry
• Nucleus—Central region in which most of the mass is
concentrated
– Protons
• Mass = 1
• Charge = +1
• Responsible for the atomic number
• Controls the name of the element
– Neutrons
• Mass = 1
• Charge = 0
Basic Chemistry
– Atomic Mass Number
• The number of protons plus the number of neutrons
• Changing the number of neutrons changes the atomic mass without changing
the atomic number or the element
• Produces isotopes —atoms with the same atomic number but a different mass
– Atomic weight—mass of the average atom
• Takes into account the relative abundance of isotopes
• Does not have to be a whole number
Basic Chemistry
• Electron cloud
– Zone of rapidly moving electrons
– Electrons
• Mass 0
• Charge = -1
• Arranged in energy levels or shells
– The outermost electron shell is the most important one in controlling chemical reactions
and in making atoms link together or bond
– Except for atoms having only 1 shell, the desirable configuration is 8 electrons in the
outermost shell (oversimplification!)
– Atoms are stable when electrically neutral—the number of protons
equals the number of electrons
Bonding
• An atom with 2 electrons in the outermost shell will lose them
rather than gain 6
– This makes it an atom with extra protons and a charge of +2
– A charged atom is an ion; one with a positive charge is a cation
(attracted to the cathode or negative electrode in a cell)
– Major cations are Si, Al, Fe, Mg, Ca, Na, K
– Negatively charged ions are anions (attracted to the anode or positive
electrode in a cell)
– Major anions are O, Cl, OH, F
Bonding
• Ionic Bonds
– Oppositely charged ions attracted to each other
– Dissolve in polar solvents
– Moderately hard crystals
– Moderate specific gravity
– High melting and boiling points
– Poor conductors of heat an electricity
– Ionic size and charge are important
– Most minerals
Bonding
• Covalent Bonding
– Electron sharing
• Common in elements with ~ 4 electrons in outermost shell
• Carbon is probably the best example
• Cl – Cl or Cl2 is another
– Commonly insoluble
– Very stable
– Very strong bond
– Very high melting and boiling points
– Bonding is highly directional
Bonding
• Most bonds are somewhat covalent and somewhat ionic
• Metallic bond
– An extreme form of electron sharing
– Weak bond
– Easy rearrange which explains why metals can be shaped so easily
– Explains electrical conductivity
• Van der Waal’s forces—extremely weak bond
What Is a Mineral?
• Naturally occurring
• Inorganic
• Solid
• Orderly internal arrangement of atoms
• Reasonably definite chemical composition
Mineral Properties
• Crystal Form
– Consequence of orderly internal arrangement of atoms
– Crystals of different substances have different shapes
– Angles between corresponding pairs of faces are equal
– Habit—distinctive forms
• Cubic
• Fibrous
• Color
Mineral Properties
• Luster—The way a mineral reflects light
– Metallic
– Sub-metallic
– Non-metallic
• Adamantine
• Vitreous
• Pearly, greasy
• Dull, earthy
Mineral Properties
• Cleavage
– The way a mineral breaks
– Refers to breakage on flat planes that reflect light
– Described by number of planar directions and angle between planes
• 1 direction
• 2 directions at right angles
• 2 directions not at right angles
• 3 directions at right angles
• 3 directions not at right angles
• 4 (or more) directions
Mineral Properties
• Hardness—Moh’s Scale
– 1 = talc 6 = feldspar
– 2 = gypsum 7 = quartz
– 3 = calcite 8 = topaz
– 4 = fluorite 9 = corundum
– 5 = apatite 10 = diamond
• Steps are not equal
– Difference between corundum and diamond is greater than the whole
rest of the scale
Mineral Properties
• Hardness of common objects
– 2 - 3 = fingernail
– 3 = penny
– 5 - 5½ = steel
– 6 - 6½ = glass
• Streak—The color of a fine powder left when the mineral is
rubbed against a piece of unglazed porcelain
Mineral Properties
• Density
– Mass per unit volume
• Hard to measure volume of irregular shape
• Used Archimedes principle
• WA/(WA-WW) = Specific Gravity
•
Because water has a density of 1.0 g/cm3, specific gravity is numerically equal
to density in g/cm3
– Most minerals have densities around 2.5 -3.0
– Minerals that are significantly denser are easy to recognize