Minerals A. Changing scales to looking at the elements of the earth and its crust (8 most common) B. Introduction to minerals that comprise rocks (11 most common minerals) C. The silicate minerals (7) D. Other important rock-forming minerals (4) E. Mineral properties

Biotite Quartz Feldspar A. Changing Scale: Zooming in from global view to atomic scale The crust is made of rocks > Rocks are made of minerals > …

Rocks  Minerals  Atoms Fig. 2.1 Fig. 2.3 Fig Fig. 2.17a Fig Fig. 2.7 Quartz Feldspar Biotite

The Elements of the Crust and Where They are Found O and Si make up most of the earth’s crust (including oceanic) O, Si, Al, Na and K are more abundant in the Continental Crust Fe, Mg, and Ca are much more abundant in the Oceanic Crust Fe and Mg make up more than half of the Mantle <1 35 <1 10 ~8 Incr.  Dcr.  Incr.  Dcr.  Whole Earth (proto-earth) Percentage Crustal Change in crust due to differentiation O and Si make up most of the earth’s crust (including oceanic) O, Si, Al, Na and K are more abundant in the Continental Crust Fe, Mg, and Ca are much more abundant in the Oceanic Crust Fe and Mg make up more than half of the Mantle     

Atoms and Elements Nucleus Protons + Charge Has Mass, Atomic # Neutrons 0 Charge Mass similar to One Proton Atomic Mass # Electrons In shells (2, 8, 8…) - charge (balances each proton +) Very little Mass

Ions and Bonding Incomplete electron shells tend to be filled E.g. Chlorine (Cl - ) 17 protons (at.# 17) 17 electrons would make it neutral (no charge) with the last shell one electron short {2, 8, 7} Soooo… Tends to grab an electron to fill the third shell Making it a negatively charged Ion (anion)

Ions and Bonding (cont.) Other Common Examples Sodium, at.# 11 {2, 8, 1}  Na + Oxygen, at.# 8 {2,6},  O -2 Silicon, at.# 14 {2,8,4}  Si +4 Fig. 2.3 Oxygen (O -2 ) Fig. 2.5 (Cation)

B. Introduction to Minerals Halite Mineral mined for rock salt and table salt Na gives electron to Cl Opposites attract, elements bond NaCl (Sodium Chloride)

Intro to Minerals Repeating 3-D pattern forms a Crystalline Solid (or Crystal) Naturally occurring crystals are Minerals Crystalline structure and bonding leads to physical properties: hardness, crystal form, cleavage  specific gravity (density) Fig Fig Crystal Form  (Habit) 3 planes of cleavage

Quartz Crystal (SiO 2 ) Snow Flake (Ice Crystal) due to crystalline structure of H 2 O Some Familiar Crystal Forms Fig. 2.15a

Definition: Mineral a. Crystalline solid b. Naturally Occurring (not artificial) c. Definite chemical composition some unique Many with a definite range of composition (mineral groups)

C. Silicate Minerals Silica: The chemical compound of Silicon and Oxygen Oxygen and Silicon are the most abundant elements in the earth’s crust, thus Silicate Minerals are a class of minerals that comprise most (>90%) of the crust Continental Crust is higher in silica Oceanic Crust is lower in silica

Silica Tetrahedra and Silicate Minerals One Si and Four O s bond in a tetrahedron shape The silica tetrahedron is the basic building block of most minerals of the crust Silica tetrahedra bond with other tetrahedra by sharing Oxygens Other cations bond to form a wide variety of Silicate Minerals Fig. 2.7 Fig. 2.8 Fig SiO 3 -2

Silicate Minerals (cont.) E.g., Olivine Isolated silicate structure Bonded with iron and magnesium Makes up much of the mantle Fe/Mg rich >50% [2:7] Silica poor <45% [1:7] Fe 2 (SiO 4 ) to Mg 2 (SiO 4 ) Ferromagnesian Mineral [2:7] Numbers in Square Brackets are atomic ratios. E.g. 2 atoms Fe to total number of atoms

Silicate Minerals (cont.) E.g., Pyroxene (Group of minerals) Single Chain Silicate structure bonded with Fe, Mg, Ca, and Al Found in Oceanic Crust Fe/Mg/Ca rich [1:5] Silica poor [1:5] X SiO 3 X = Fe +2,Mg +2, Ca +2, and Al Also a Ferromagnesian Mineral SiO 3 -2 Cleavage and Form Prismatic

Silicate Minerals Other Important examples Olivine: most of mantle Pyroxene: Oceanic Crust* Amphibole: Continental Crust Micas: Biotite, Muscovite continental crust Clay: In many soils Na and K Feldspar: Continental Crust Ca Feldspar: Oceanic Crust* Quartz: Continental Crust and many soils Olivine Pyroxene Group Amphibole Group Mica Group Clay Group Quartz Feldspar Group Isolated Silicate Structure Single Chain Structure Double Chain Structure Sheet Structure Framework Structure Silicate Structure Example

Fig. 2.9 From bottom to top Increasing Fe/Mg/Ca Decreasing silica Increasing density Darker minerals Decreasing Silica 1:3½ 1:7 1:5 1:5 <1:35 1:4 1 / 3 <1:40 1:4 (0) 1:3 (0) 1:4 1 / 3 (0) 1:6 ½ Ratio of Tot. Atoms to :Iron :Silicon Increasing Fe/Mg/Ca Quartz K and Na Feldspar Ca Feldspar Systematic Silicate Mineralogy Increasing Density Olivine Pyroxene Group Amphibole Group Mica Group

Fig. 2.9 From bottom to top Increasing Fe/Mg/Ca Decreasing silica Increasing density Darker minerals Fe/Mg/Ca Density Weathering* Quartz K and Na Feldspar Ca Feldspar # Systematic Silicate Mineralogy Olivine Pyroxene Group Amphibole Group Mica Group Melting and crystallizing Temperature ~ Increasing Decreasing *All of these silicates weather to form Clay Minerals Except quartz ~ Quartz melts first Mantle Oceanic Crust # Cont. Crust

Other Important Rock-Forming Minerals Sediments and Sedimentary Rocks Quartz: resistant to alteration by weathering Clay: most other silicates weather to clay Carbonates (non-silicates): Deposited in shallow tropical seas be shellfish and coral Calcite: CaCO 3 Dolomite: CaMgCO 3 Halite: Deposited by evaporating seas Single Element Minerals: Diamond, Graphite, Gold, sulfur