UNIT 2: Earth Materials

Overview of the Unit Minerals: -definition -formation -types -identification/tests Rocks: -definition -formation and rock cycle -categories/types -identification Materials as a resource -mining (oral presentation)

First… a review of basic chemistry Atoms are composed of a dense nucleus containing protons and neutrons that is orbited by electrons. The number of protons indicates what element it is. These electrons orbit in distinct energy levels (shells). Each shell can only have a specific number of electrons before it becomes full and a new shell must be started. The electrons in the outermost shell are called valence electrons. The number of valence electrons dictate how the elements react. Remember: atoms want full valence shells, either by gaining or losing electrons (ionic bonds), or by sharing electrons (covalent bonds).

A closer look at ionic bonds When a metal and a non-metal bond, the metal will transfer 1 or more electrons to the non-metal so that they both have full valence shells. The result is that the positive metal ion is attracted not only to the negative non-metal ion it gave its electron(s) to, but also all the other non-metal ions. This results in a crystal lattice structure.

More on crystals... Not all crystals take this shape. (Only ionic compounds in a 1-1 ratio like NaCl) Other ionic compounds not in 1-1 ratios (ie. BeCl2) may have different structures. Even some covalent bonds result in the formation of crystals (diamond, for example, which is just a carbon crystal).

Properties of Crystals The bonds between ions in the same plane are quite strong, but the attraction between planes may not be. As a result, crystals generally appear to have very distinct shapes.

Minerals Definition: A mineral is a naturally occurring, inorganic, solid element or compound with definite composition and regular internal crystal structure.

Classifying Minerals Surprisingly, using colour to classify or identify a mineral is usually not appropriate. The reasons for this are 1) Many minerals may have the same colour for different reasons 2) The same mineral may be found in several different colours due to impurities inside the mineral. Example: Pure corundum is colourless, and is often used as grit in sandpaper. When colour is added we get... Red --> rubies Blue --> sapphire

Classifying Minerals Minerals can be classified based on two properties... 1) composition 2) crystal structure Here are some common groups…

Silicates: composed of silicon and oxygen and often other elements most common minerals (since Si and O are the two most common elements in Earth’s crust) subdivided based on crystal structure (we won’t go into details here) Some common examples: quartz (SiO2) --> used to make glass also found in some watches with a purple tint (impurities) it is called amethyst feldspars --> also contain Al + either Na, K, or Ca ferromagnesians --> also contain Fe and/or Mg clays --> sheets of Si and O stacked on each other weak bonds between sheets, thus slippery may absorb water and expand

Silicates Quartz Feldspar - nepheline (Na, K, Al, Si, O) Amethyst Clay - talc (Mg, Si, O, OH) Ferromagnesian - biotite (K, Fe, Mg, Al, Si, O, OH, F)

Some Non-Silicates Carbonates metals + CO3 most common carbonate is calcium carbonate (CaCO3) Note: Calcite is a group in the form of XCO3 where X is an element in the same group as Ca. Sulfates metals + SO4 Example: gypsum (calcium sulfate with water, CaSO4(2H2O))

Some Non-Silicates Sulfides metals + S (no O) Example: pyrite (fools gold) Oxides metals + O Examples: corundum (Al2O3) magnetite (Fe3O4) hematite (Fe2O3)

Some Non-Silicates Hydroxides metals + OH Example: gibbsite (Al(OH)3) Halides metals + a halogen Example: halite (NaCl) Native Elements any mineral consisting of a single element Example: gold