EPS 101 Spring 2003 – Dr Adrian Brearley - Lecture 5

High resolution electron microscope image of diamond.

Minerals - Building blocks of rocks II

Keywords and concepts

Chemical behavior of the elements

Chemical reactions – interactions between two or more atoms to produced new chemical substances – compounds.

Ion – atom that has lost or gained an electron or electrons and has either a positive or negative net charge.

Cation – ion with a positive charge, e.g. Na⁺, Ca²⁺

Anion – ion with a negative charge, e.g. Cl^-, SO₄^2-

Electron shells – series of shells surrounding the nucleus of atoms. Each shell can contain a specific number of electrons.

Electron sharing – atoms of the same or different elements sharing electrons in order to form a chemical bond.

Periodic Table – table that organizes the elements into groups according to their chemical properties.

Chemical Bond – force that binds atoms together in compounds.

Ionic Bond – formed by electrical attraction between ions – e.g. Na⁺ and Cl^- to form NaCl.

Covalent Bonds – Formed by elements that don’t readily form ions. Formed by sharing of electrons between atoms.

Metallic bond – found in metals – freely mobile electrons shared and dispersed between metal ions.

Structure and properties of minerals

Crystallization – process by which a solid material forms as constituent atoms come together in the proper chemical compositions and crystalline arrangement. Forms crystals. Crystallization can occur in many ways – from a cooling magma at high temperatures, by precipitation from a solution at low temperature, etc.

Precipitation – process by which minerals crystallize from a solution as evaporation occurs.

Packing – the way in which ions of different sizes fit together in mineral crystal structures. Anions tend to be large and the smaller cations fit in the spaces between them.

Cation substitution – cations of similar sizes and charges may substitute for one another in the same crystal structure. e.g. olivine (Mg,Fe)₂SiO₄ where Mg and Fe can substitute for one another.

Polymorphs – different crystal structures of the same chemical compound e.g. graphite and diamond, polymorphs of carbon.

Rock-forming minerals

Silicates – composed of oxygen (O) and silicon (Si) in combination with other cations, e.g. olivine (Mg,Fe)₂SiO₄.

Carbonates – minerals made up of the carbonate ion (CO₃)^2- in combination with other cations (mainly Ca and Mg) e.g. calcite CaCO₃.

Oxides – compounds consisting of oxygen and metallic cations e.g. magnetite Fe₃O₄.

Sulfides – compounds of the sulfide anion (S^2-) and metallic cations e.g. pyrite FeS₂.

Sulfates – compounds of the sulfate anion (SO₄)^2- and metallic cations e.g. anhydrite (CaSO₄).