Earth’s Materials and Processes-Part 6 Minerals

Minerals Naturally occurring, solid, crystalline substance. Generally inorganic. Has a specific chemical composition. Arranged in a repeating 3-D array (crystalline) Building Blocks of Rock

Atomic Structure Ionic Bonds: electrical attraction between ions of opposite charge. Strength increases with the electrical charges of ions. Bond strength decreases as distance between bonds increases. Most minerals contain ionic bonds. Ex: Halite (NaCl)

Atomic Structure Covalent Bonds Electrons are Shared Generally stronger than ionic bonds.

Crystallization of Minerals Need a starting material with atoms that can come together in the proper proportions. Ex: Growth from a liquid or a gas. Time and space for crystallization. Appropriate temperature and pressure. Examples: Magma that has cooled. Supersaturated solution  precipitation reaction. Crystal begins as an initial, microscopic crystal. Atoms continue to be added in a 3-D array, repeating in the basic arrangement. Crystal faces are based on the array structure.

Cations and Anions Cations (positively charged) ions are typically relatively small. Anions (negatively charged) ions are typically large. Crystal structure is determined largely by the arrangement of cations and of the anions.

Compound Ions Many common minerals are silicates. Complex ions act as a single ion in forming a crystal structure. Example: Silicate Ions (SiO44-)

Cation Substitution Crystal structure determined by large cations. Cations can substitute for each other in other minerals. Same crystal structure Different chemical composition Polymorphs: Minerals with the same composition, but different chemical structure.

Example

Common Rock-Forming Minerals

Silicates Most abundant mineral in Earth’s crust. Silicate ion (SiO44-) Includes: Quartz, K-Feldspar, Olivine

Carbonate Cations with carbonate ions (CO32-) Calcite, Dolomite, Siderite, Smithsonite. Make up many common rocks including limestone and marble.

Oxides Compounds of metallic cations and oxygen. Important for many metal ores needed to make things (iron, chromium, titanium) Economically Useful (possible to mine)

Sulfides Metallic cations with sulfide (S2-) ion Important for ores of copper, zinc, nickel, lead, iron. Examples: Pyrite, Galena,

Sulfates Minerals with sulfate ion (SO42-) Example: Gypsum

Identification of Minerals Chemical composition Crystal Structure Physical Properties Hardness

Mohs Scale Used to measure mineral hardness.

Physical Properties Cleavage: tendency of minerals to break along flat, planar surfaces into geometries that are determined by their crystal structure. Fracture: Tendency to break along other surfaces (not cleavage planes). Luster (metallic, earthy, etc.) Color (often a poor indicator, streak color is better). Specific gravity Crystal habit (shape).