Minerals Lecture

MINERALS LECTURE

Elements Substances that cannot be broken down into stable material by any means. Identified as kinds of atoms. Minerals Solid, naturally occurring earth materials with crystal structure and definite chemical composition Rocks Solid, naturally occurring components of our plant that occur as masses and are almost always composed of different combinations of minerals. Rare and atypical rocks, composed of non-mineral materials include obsidian, pumice [glassy volcanic rocks] and coal [metamorphosed organic material].

Structure and Properties of Atoms Nucleus PROTONS - dense, positively charged No. of protons = ATOMIC NUMBER of the element NEUTRONS- same mass, no charge ELECTRONS Negative electronic charge Orbit the nucleus, forming “clouds” Shells or energy levels Outermost shell - VALENCE ELECTRONS – bonding Naturally, atoms have the same number of protons and electrons Bonding Valence electrons range from 1 (eg. H, Na, K), to 8 First shell has 2 Otherwise, valence shell is stable when it has 8 electrons (Noble gasses have 8, and are INERT)

Chemical Bonds Result in full shell of 8 electrons Transferred = Shared =

IONIC bond COVALENT bond

Ionic Bonding Transfer of electrons to another atom, filling its shell, Eg. Na and Cl Note that after transfer, the atoms are now charged Na+ and ClCharged atoms are called IONs , and when bonded they form IONIC COMPOUNDS These are ions that are regularly arranged, and have an overall neutral charge. They have dramatically different properties than their formative elements – eg NaCl Ionic bonds are very weak, and often may be broken by dissolving the ionic compound in water.

Covalent Bonds Result of atoms sharing electrons Eg. O2, H2 and Cl2 are stable, naturally occurring molecules Example: Chlorine molecule, with shared pair of electrons; Note that both atoms now have full outer shells of 8 electrons These are much stronger bonds than ionic bonds The silicate minerals, most common, have many covalent bonds between Silicon and Oxygen LOOK at dot diagram, how many oxygens would have to bond with Si to form a stable molecule? We’ll see SiO4 again soon. Metallic Bonding Valence electrons migrate freely between the atoms

Metallic ions form many other complex molecules that are important to mineralology.

Isotopes and Radioactive Decay The mass number of an element is the total weight of its protons and neutrons These each have about 1 atomic mass unit of weight, whereas An electron has about 1/2,000 of an AMU Isotopes= Elements with the same number of protons, but different numbers of neutrons Two kinds: Eg.:

stable and radioactive

Carbon has three isotopes; all have 6 protons and 4 valence electrons: 12 C, 13C = stable carbon 14

C

=

radiocarbon

Radioisotopes decay through time. The rate of decay is given by the half-life of the isotope, the time for half of the mass to be lost to decay. 14

C to K to

40

14

N = 5730 years Ar = 1.3 billion years

40

important for dating in geology.

Mineral Properties Hand Specimen

In Field

Color Crystal form Cleavage Hardness Fracture Reaction to HCl Luster Streak Specific gravity

Color/luster Cleavage Hardness Reaction to HCl

Mineral Groups Silicates Light Quartz Feldspar Group Clay minerals Dark Olivine Pyroxene group Amphibole group Micas Biotite Muscovite Oxides Carbonates Sulfates Halides Sulfides Native Elements