A naturally occurring, inorganicsolid with an ordered internal structureand a narrow range of chemical composition. Mineral
Rock A naturally-occurring consolidated mixture of minerals or mineral-like substances.
A rigid sphere about 1 angstrom (Å) in diameter (angstrom is 10-10 m). At the center of an atom is a nucleus which contains most of the mass of the atom. Protons (positive charge) Neutrons (no charge -- neutral) Electrons (negative charge) orbit the nucleus. Atoms
Electrons(E): negative charge, very little mass Protons(Z): positive charge, mass 1832x greater than electron Neutrons(N): no electric charge, mass 1833x greater than electron Atoms
Atomic Number: Number of protons in an atom Atomic Mass: Sum of the masses of the protons and neutrons in an atom. 12C = carbon-12 (6 protons and 6 neutrons) 13C = carbon-13 (6 protons and 7 neutrons) 14C = carbon-14 (6 protons and 8 neutrons) Atoms with the same number of protons and different numbers of neutrons are called isotopes. Atoms
Electrons orbit around the nucleus in discrete shells. Atomic structure Nucleus: protons, neutrons Fig. 3.2
C-12 Fig. 3.2
Electron Cloud Fig. 3.2
First level (K) 2 electrons Second level (L) 8 electrons Third level (M) 18 electrons Fourth level (N) 32 electrons Energy-level shell:the space occupied by electrons of a particular energy level Atoms are MOST STABLE when their outer electron shell is filled.
Atoms join with other atoms to try to fill their outer shells. Two types of bonds: Ionic bond: Formed by the electrical attraction of ions of opposite charge. 90% of minerals are formed through ionic bonds. Covalent bonds: Formed by sharing electrons. Metallic bonds are one type of covalent bond. Diamonds. Bonding
Ion • An electrically charged particle composed of an atom that has either lost or gained electron(s) to or from another atom. • When an atom loses or gains an electron it is called an ion. • Positively charged ions (loss of electron) are called cations. • Negatively charged ions (gain of electron) are called anions.
Important ions in minerals anions charge cations charge Si +4 K +1 Ca +2 Na +1 Al +3 Mg +2 Fe +2 or +3 O -2
Ionic Attraction Forms NaCl (Halite) Fig. 3.4
Halite Fig. 3.4
Halite close-up Fig. 3.6
Electron Sharing in Diamond Fig. 3.5
Crystal: Ordered three-dimensional arrays of atoms in which the basic arrangement is repeated in all directions. Crystals Fig. 3.8
Crystallization: The growth of a solid from a gas or liquid whose constituent atoms come together in the proper chemical proportions and crystalline arrangement. When do minerals form? Crystallization from a magma Crystallization from a pre-existing solid phase Precipitation from solution (halite, evaporation) How do minerals form?
Crystal face: Boundaries of crystals. Natural flat (planar) surfaces. External expression of a mineral’s internal atomic structure. Perfect crystal: Crystal for which crystal faces are easily observed. Requires crystallization under special conditions (e.g., enough room to grow). Crystals
Quartz Geode Large space allows larger crystals
Graphite Atomic Structure Crystal Form After Fig. 3.11
Diamond Atomic Structure Crystal Form After Fig. 3.11
Polymorphs • Minerals with the same chemical composition but different structure. • For example • diamond (3.5 g/cm3) and graphite (2.1 g/cm3) • andalusite, kyanite, and sillimanite
There are some 3,500 recognized minerals found on Earth. However, For our purpose, we can focus on about a dozen. Groups: Silicates. Si, O and other elements. Most abundant mineral group in the Earth’s crust (>75%). Carbonates. Ca, Mg and CO3 Halides or Salts. NaCl Sulfides. Sulfide anion (S2-) and a metallic cation. Oxides. O and a metallic cation. Minerals: lots and lots of ’em
Important mineral groups Name Important constituents • Silicates • Olivine Si, Fe, Mg • Pyroxene Si, Fe, Mg, Ca • Amphibole Si, Ca, Mg, Fe, Na, K • Micas Si, Al, K, Fe, Mg • Feldspars Si, Al, Ca, Na, K • Carbonates C, Ca, Mg • Sulfides Fe, Cu, Zn, Ni • Oxides Fe, Al
Building blocks of silicate minerals Four oxygens surrounding a silicon ion. These tetrahedra combine to make the framework of the silicates. Different combinations produce different structures. Silica-oxygen tetrahedra
Silicate Ion[SiO4] 4+ Fig. 3.11
Olivine Isolated Tetrahedra Silcate (example: olivine, (Mg,Fe)2SiO4) Fig. 3.11
Some Silicate Minerals Mica Feldspar Olivine Pyroxene Quartz
Oxides Hematite, Fe2O3 Corundum, Al2O3 Magnetite, Fe(II)Fe(III)2O4
Sulfates Galena, PbS Gypsum, CaSO42H2O Pyrite, FeS2
Carbonates Dolomite, CaMg(CO3)2 Calcite, CaCO3
Feldspar (~60% of crust): NaAlSi3O8, CaAl2Si2O8 Quartz (~12% of crust): SiO2 Important Crustal Minerals Oxygen (O) 46.3% Silicon (Si) 28.2% Aluminum (Al) 8.2% Iron (Fe) 5.6% Calcium (Ca) 4.1% Sodium (Na) 2.4% Potassium (K) 2.1% Magnesium (Mg) 2.3% Titanium (Ti) 0.5% Nickel (Ni) trace All others trace
Olivine (~60% of upper mantle): (Mg,Fe)2SiO4 Clinopyroxene (~25% of upper mantle): Ca(Mg,Fe)Si2O6 Orthopyroxene (~10% of upper mantle): (Mg,Fe)SiO3 Garnet (~5% of upper mantle): X2Y3Si3O12, where X = Ca, Fe, Mg, or Mn, and Y = Al, Cr, or Fe Important Mantle Minerals Oxygen (O) 29.5% Silicon (Si) 15.2% Aluminum (Al) 1.1% Iron (Fe) 34.6% Calcium (Ca) 1.1% Sodium (Na) 0.6% Potassium (K) 0.1% Magnesium (Mg) 12.7% Titanium (Ti) 0.1% Nickel (Ni) 2.4% All others 2.7%
Solid Solution • Like solutions, minerals can have a range of compositions. • Continuous range of mineral compositions is called solid solution. • The range in composition is created because at a single location in the crystal, several elements are permitted. • Example: • Olivine (Mg,Fe)2SiO4 • Elements between parentheses indicate a substitution • End members: Fosterite (Mg2SiO4) and Fayalite (Fe2SiO4).
IonicRadiusandCharge Fig. 3.7
Color Crystal form Density Hardness Cleavage Streak Mineral identification In hand specimen
A measure of the ease with which the surface of a mineral can be scratched. Hardness
The tendency of a crystal to break along flat, planar surfaces. Cleavage
Cleavage Atomic Structure of Micas Fig. 3.17