Minerals Chapter 2 Instructor : Pete Kozich Earth Science 101 Minerals Chapter 2 Instructor : Pete Kozich

Minerals: the building blocks of rocks Definition of a mineral Natural Inorganic Solid Possess an orderly internal structure of atoms Have a definite chemical composition Rock – any solid mass of mineral, or mineral-like material that occurs naturally

What is a Rock? An aggregate (mixture) of minerals Each mineral within the rock retains its own identity Note a large quantity of one mineral may also be considered a Rock Calcite—the rock, limestone

Composition and structure of minerals Elements Basic building blocks of minerals Over 100 are known Some minerals are made of entirely one element (e.g., Gold, Sulfur) Most individual elements are unstable Most minerals are a combination of two or more unstable elements that form a stable compound Atoms Tiny particles of matter Retains all the characteristics of an element There are more atoms in an 8 oz glass of water than there are grains of sand on all the beaches in the world and more atoms in a mole than stars in the universe!!

Periodic table of the Elements Figure 2.4

Varying mass number of Elements Isotopes A variation of an element Have varying number of neutrons but the same number of protons Have different mass numbers – the sum of the neutrons plus protons Many isotopes are radioactive emit energy and particles Unstable

How atoms are constructed Empty space occupies the greatest volume of any atom. Nucleus – central part of an atom that contains Protons – positive electrical charges Neutrons – neutral electrical charges Energy levels, or shells Surround nucleus Contain electrons – negative electrical charges

Simplified view of the atom Figure 2.5

How atoms are constructed Atomic number is the number of protons in an atom's nucleus Determines the name and nature of the element 6 Protons = Carbon, 8 Protons = Oxygen Neutral atoms have the same number of protons and electrons (charges balance) Bonding of atoms Forms a compound with two or more elements H20, CH4, NaCl Most are not easily separable Elements do not maintain individual characteristics Ionic Bond – transfer of electrons Ions are atoms that gain or lose electrons If they lose an electron – they have a positive charge If they gain an electron – they have a negative charge Covalent Bond – atoms share electrons

Chemical Bonds Bonds. Chemical bonds join atoms. We will look at 2 out of the four types of chemical bonds. Atoms of any element want their electron shells full or stable. Ionic Bonds Each element has a different number of protons. A stable electron shell may result in a different number of protons than electrons. Ionic bonds result from negative and positive ions bonding together from attraction and fill their electron shells. Covalent Bonds Atoms that are not electrically charged which share electrons to fill their electron shells.

Minerals Physical properties of minerals Crystal form Luster Color External expression of a mineral’s internal orderly arrangement of atoms Needs sufficient space and time to form Luster Appearance or quality of light reflected from a surface of a mineral Metallic, non-metallic, vitreous (glassy), pearly, silky, resinous, earthy (dull) Color Use cautiously as slight impurities in the mineral can change its color Streak Color of a mineral in its powdered form Found using a “streak plate” As a whole, much more useful than apparent color of the mineral

The mineral quartz often exhibits good crystal form

Pyrite (fool’s gold) displays metallic luster Figure 2.10

Minerals Physical properties of minerals (continued) Hardness Cleavage Resistance of a mineral to scratching One of the most useful properties Cleavage The tendency of a mineral to cleave/break along planes of weak bonding Results in pieces that have similar geometry Tends to form straight/smooth surfaces Described by the number of planes exhibited and the angles at which they meet Fluorite (four planes) Halite (three planes at 90 degrees) Calcite (three planes at 75 degrees)

Mohs scale of hardness

Three examples of perfect cleavage – fluorite, halite, and calcite

Minerals Physical properties of minerals Fracture Specific gravity Minerals that do not exhibit cleavage when broken are said to fracture (opal, for example) Fracture irregularly (Conchoidal Fracture – breaking in a glasslike manner) Specific gravity Compares a mineral’s weight with that of an equal amount of water Example: If a volume of a mineral weighs three times more than the same amount of water, then that mineral has a specific gravity of 3.0 Other useful mineral properties Taste Smell Elasticity Malleability Feel Magnetism Double Refraction Reaction to hydrochloric acid

Conchoidal fracture Figure 2.15

Minerals A few dozen minerals are called the rock-forming minerals The eight elements that compose most rock-forming minerals are oxygen (O) silicon (Si) aluminum (Al) iron (Fe) calcium (Ca) sodium (Na) potassium (K) magnesium (Mg) Most abundant atoms in Earth's crust are oxygen (46.6% by weight) and silicon (27.7% by weight) O and Si are nonmentals, Fe a transition metal, rest are metals

Composition of continental crust Figure 2.16

Minerals Mineral groups Rock-forming silicates Most common mineral group Contain the silicon-oxygen tetrahedron (molecule) Four oxygen atoms surrounding a much smaller silicon atom Combines with other atoms to form the various silicate structures Formation Crystallize from molten materials as it cools Form from weathering of other silicates (clay) Form from extreme pressure

The silicate (SiO4)-4 molecule Figure 2.17

Minerals Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Olivine – independent tetrahedra Pyroxene group – tetrahedra are arranged in chains Amphibole group – tetrahedra are arranged in double chains Micas – tetrahedra are arranged in sheets Two types of mica are biotite (dark) and muscovite (light) Feldspars - Three-dimensional network of tetrahedra Most plentiful mineral group Two types of feldspar are Orthoclase and Plagioclase Quartz – three-dimensional network of tetrahedra

Hornblende – a member of the amphibole group

Potassium feldspar

Plagioclase feldspar

Minerals Mineral groups Nonsilicate minerals Major groups Oxides Sulfides/Sulfates “Native” elements Gold, Diamonds, Graphite Carbonates A major rock-forming group Found in the rocks limestone and marble Halite (table salt) and gypsum (plaster) are found in sedimentary rocks Many have economic value

Native Copper

Minerals Mineral resources Reserves Ores Already identified deposits Ores Useful metallic minerals that can be mined at a profit Economic factors may change and influence a resource

An underground halite (salt) mine