Earth Chemistry and Minerology

Matter Matter: anything that has mass and volume Element: substance composed of atoms; can not be broken down 10 most common elements in Earth’s crust : – Oxygen (O)- Silicon (Si) – Aluminum (Al)- Iron (Fe) – Calcium (Ca) - Sodium (Na) – Potassium (K)-Magnesium (Mg) – Titanium (Ti)- Hydrogen (H)

92 naturally occurring elements – the rest are made in a laboratory.

The Structure of an Atom The nucleus is made up of the protons (positively charged molecules) and neutrons (no charge) – The number of protons and neutrons makes up the atomic number The electrons (negatively charged molecules) orbit, or circle, the nucleus.

Atomic number – equals number of protons Symbol – one or two letter abbreviation Name – elements common name Atomic mass weighted average of all isotopes

Periodic table – a tool used to organize information about the elements pp

What is a Mineral? All rocks and minerals of Earth’s crust consist of elements Mineral has the following characteristics: – Occurs naturally – Solid – Has a definite chemical composition – Its atoms are arranged in an orderly pattern – Inorganic (never alive) 4,000 known minerals

Eight most common elements found in in minerals: Oxygen O- Calcium Ca – SiliconSi- Sodium S – Aluminum Al- Potassium K – IronFe- Magnesium Mg Most minerals are compounds

Minerals can form in several ways. 1. Many form out of molten rock Example: Granite

– 2. New minerals also form when existing minerals are transformed by heat, pressure or chemical action Example: Hornblende Schist

3. Precipitation – solids form from super saturated solutions. Ex calcite and halite 4. Hydrothermal solutions – dissolved elements react with each other in very hot water causing chemical reactions which form new minerals.

Structure of Minerals Crystal: a regular geometric solid with smooth surfaces called crystal faces – By definition, all minerals have crystalline structures (regular, orderly arrangements of atoms) Crystal Structure: – The angle at which crystal faces meet is characteristic for each type of mineral and can be used to help identify the mineral – Six basic types of shapes

Cubic System Orthorhombic System Tetragonal System Triclinic System Hexagonal Structure Monoclinic Stucture

Silicates: Minerals that include compounds of silicon and oxygen. More than 90% of the minerals in Earth’s crust are silicates

Silica tetrahedron : basic building block of a silicate – Four oxygen atoms packed closely around a silicon atom

Crystal Structure and Physical Properties The temperatures at which a mineral melts and vaporizes is individual to that mineral

Significance of crystal structure Example of the relationship between hardness and crystalline structure: The following two minerals are both pure Carbon. – Diamond: Atoms arranged in tetrahedral network – hardest natural mineral – Graphite: atoms arranged in sheets of hexagonal networks – soft and flakes easily

Identifying Minerals Mineralogy: study of minerals and their properties Minerals can be identified and classified by inspecting them visually and performing simple tests to determine their properties

Identifying Minerals by Inspection Color the most easily observed property Least useful for mineral ID – Minerals may have similar colors – Impurities and other factors can change colors

Calcite

Luster: the way the mineral shines in natural light Metallic – shiny metal reflection

Non-Metallic

Non-metallic may shine like glass.

Testing Mineral Specimens – Certain characteristics can be tested for. – Streak – Cleavage – Hardness – Specific gravity

Streak The color of a mineral’s powder Although the color of a mineral may vary, the streak rarely does

Cleavage The tendency to split along definite planes – The planes along which the mineral splits correspond to planes of weak bonds between atoms, ions or molecules

Fracture – If a mineral does not cleave, it fractures. An uneven breakage that can occur anywhere on the mineral.

Hardness Hardness of a mineral is its resistance to being scratched – Diamond: hardest of all minerals – Talc: softest of all minerals Hardness of a mineral depends on: – arrangement of its ions, atoms or molecules – strength of the chemical bonds between them

Mohs Scale of Hardness – 10 well-known minerals are assigned numbers 1-10

In most cases, a person can determine the approximate hardness of any common mineral by using your fingernail, a copper penny, a small glass plate and a steel file

Specific Gravity: ratio of a minerals mass to the mass of an equal volume of water – Tells you how many times denser the mineral is than water – Use a spring scale to measure – Buoyancy: tendency of an object to float in water due to the differences in densities b/t the water and the object

Special Properties Some minerals have unusual characteristics that can help ID the mineral Taste like salt Magnetic properties Reacts with HCl

Mineral Groups Silicates Quartz: Chemical Formula: SiO 2 Glassy or greasy luster Pure Quartz: colorless Colored Quartz: rose quartz, amethyst Hardness of 7 Significant component of many types of rocks

Feldspars Make up about 60% of Earth’s crust Share 3 features: – two directions of cleavage – Hardness of 6 – Pearly luster Most abundant family of minerals Important rock-forming minerals Used to manufacture glass and ceramics

Other silicates – Pyroxene: cleavage surfaces meet nearly at right angles – Micas: soft silicates; hardness of 2.5 and perfect cleavage – Amphibole: complex silicates; long, needlelike crystals – Olivine: used to make jewelry – Kaolinite: aluminum silicate; commonly used in ceramics, paints and fiberglass

Carbonates Minerals made of negatively charged carbonate ions bonded to positive metal ions All Contain CaCO 3 –Calcium carbonate All will effervesce with Hydrochloric acid HCl Calcite and Dolomite

Calcite Dolomite

Oxides Mineral consisting of a metal element combined with oxygen – Hematite and Magnetite – Sulfides – Mineral consisting of a metal element combined with sulfur – Pyrite

Hematite Magnetite Pyrite

Native Elements A group of minerals which exist in pure form. Ex. Gold, silver, copper, carbon