Chapter 3: Earth Materials: Minerals and Rocks

• What are minerals?

o Mineralogy- the branch of geology that studies the composition, structure,
appearance, stability, occurrence, and associations of minerals
o Mineral- a naturally occurring solid crystalline substance, usually
inorganic, with a specific chemical composition
 Naturally occurring
 Solid crystalline substance
• Crystalline- the tiny particles of matter, or atoms, that
compose it are arranged in an orderly, repeating, 3D array
 Usually inorganic
 Specific chemical compound
• The Structure of Matter
o The structure of atoms
 The Nucleus: Protons and Neutrons
• Nucleus contains positive (+1) protons and neutral neutrons

o Atoms of the same chemical element may have

different numbers of neutrons, but the number of
protons does not vary
o Ex. All Carbon has 6 protons
• Electrons-surrounds nucleus, negative (-1) charge
o Same number of protons and protons= balanced
nucleus of atom
 Atomic Number and Atomic Mass
• Atomic Number- the number of protons in the nucleus of
an atom
o Ex. All atoms with 6 protons are carbon atoms
• Atomic Mass- an elements is the sum of the masses of its
protons and its neutrons
o Isotopes- atoms of the same element with different
numbers of neutrons
 Ex. Carbon
• Chemical Reactions- interactions of the atoms of two or more chemical
elements in certain fixed proportions that produce chemical compounds
 Electron sharing, Ex. Carbon and Silicon, Diamonds (Carbon
Sharing)
 Electron transfer, Ex. NaCl, sodium loses one electron, which
chlorine gains
 Ion- Atom or group of atoms that has an electrical charge, either
positive or negative, because of the loss or gain of one or more
electrons
• Cation- positively charged ion
 • Anion- negatively charged ion
o Chemical Bonds
 Ionic Bonds- simplest form of chemical bon, formed by
electrostatic attraction between ions of opposite charge, when
electrons are transferred, dominant in minerals
 Covalent Bonds- elements that do no readily gain or lose electrons
to form ions, instead form compounds by sharing electrons,
stronger
• Ex. Diamond
 Metallic Bonds (type of covalent bond)- atoms of metallic
elements, which have usually lose electrons pack together as
cations and the freely mobile electrons are shared and dispersed
among those cations, free electron sharing results
• The Formation of Minerals
o Atomic Structure of Minerals
 Crystallization- the atoms of a gas or liquid come together in the
proper chemical proportions and in the proper arrangement to
forma solid substance
 Anions take up more space than cations
 Cations of similar sizes and charges can substitute for each other
• Common in Silicate ion (SiO4 ^-4)
o Crystallization of Minerals
 Begins with the formation of single crystals, 3d arrays of atoms in
which the basic arrangement is repeated in all directions
• Crystal faces- natural flat (planar) surfaces, external
expressions of the mineral’s internal atomic structure,
o How Do Minerals Form?
 Lowering liquid below freezing point, magma, evaporation
• Classes of Rock- Forming Minerals
1. Native elements- occur naturally as un-ionized pure elements
• most others are classified by their anions (copper)
2. Silicates- most common in crust, Oxygen (O) and Silicon (Si)
• SiO4^4- -> olivine (Mg, Fe)2SiO4
• Bonds to cations (na+, K+, Ca^2+, mg^2+, fe^2+
• Structures
 Isolated tetrahedral- linked by the bonding of each oxygen ion
of the tetrahedral to a cation Ex. Olivine
 Single- chain structures- formed by sharing of oxygen ions
3. Carbonates- composed of carbon and oxygen- combo with calcium and
magnesium
• CO33^2- -> calcite (CaCO4)
4. Oxides- composed of oxygen anion (O^2-) and metallic cations
• O^2- -> hematite (Fe2O3)
5. Sulfides- sulfide anion (S^2-) and metallic cations
 • S^2- -> Pyrite (FeS^2)
6. Sulfates- sulfate anion (SO4^2-) and metallic cations
• SO4^2- -> Anhydrite (CaSO4)