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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 Quartz Biotite 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. 2.7 Fig. 2.1 Fig. 2.3 Fig. 2.15 Biotite Quartz Fig. 2.17a Fig. 2.19 Feldspar The Elements of the Crust and Where They are Found O and Si make up most of the earth’s crust Crustal Crustal Change in (including oceanic) Whole Earth crust due to (proto-earth) differentiation O, Si, Al, Na Percentage and K are more abundant in the 30 Incr. Continental Crust 15 Incr. <1 Incr. Fe, Mg, and Ca 35are much more Dcr. abundant in the <1 Incr. Oceanic Crust <1 Incr. <1 Incr. Fe and Mg make up more than 10 Dcr. half of the Mantle ~8 • 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 Neutrons + Charge Has Mass, Atomic # 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+ (Cation) Oxygen, at.# 8 {2,6}, O-2 Silicon, at.# 14 {2,8,4} Si+4 Fig. 2.5 Fig. 2.3 Oxygen (O-2) 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 Fig. 2.18 Fig. 2.20 Repeating 3-D pattern forms a Crystalline Solid (or Crystal) Naturally occurring Crystal Form (Habit) crystals are Minerals Crystalline structure and bonding leads to physical properties: hardness, crystal form, cleavage specific gravity (density) 3 planes of cleavage Some Familiar Crystal Forms Quartz Crystal (SiO2) Fig. 2.15a Snow Flake (Ice Crystal) due to crystalline structure of H2O 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 SiO3-2 Fig. 2.7 Fig. 2.8 Fig. 2.11 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] Fe2(SiO4) to Mg2(SiO4) 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 SiO3 X = Fe+2,Mg+2, Ca+2, and Al Also a Ferromagnesian Mineral Cleavage and Form Prismatic SiO3-2 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 Silicate Structure Example Isolated Silicate Structure Olivine Single Chain Structure Pyroxene Group Double Chain Structure Amphibole Group Mica Group Sheet Structure Framework Structure Clay Group Quartz Feldspar Group Ratio of Tot. Atoms to :Iron :Silicon Olivine 1:3½ 1:7 Systematic Silicate Mineralogy Pyroxene Fig. 2.9 1:5 Group From bottom to top Decreasing Increasing Silica Fe/Mg/Ca Increasing Density Amphibole Group 1:5 <1:35 1:41/3 Increasing Fe/Mg/Ca Decreasing silica Mica Group Increasing density <1:40 1:4 Darker minerals Quartz K and Na Feldspar Ca Feldspar (0) 1:3 (0) 1:41/3 (0) 1:6 ½ Systematic Silicate Mineralogy Olivine Mantle Pyroxene Group Fig. 2.9 Oceanic # Crust From bottom Increasing Melting and crystallizing Temperature~ top Fe/Mg/Ca Density Weathering* Decreasing ~Quartz melts first *All of these silicates weather to form Clay Minerals Except quartz to Amphibole Group Increasing Fe/Mg/Ca Decreasing silica Mica Group Increasing density Darker minerals Cont. Crust Quartz K and Na Feldspar Ca Feldspar# 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: CaCO3 Dolomite: CaMgCO3 Halite: Deposited by evaporating seas Single Element Minerals: Diamond, Graphite, Gold, sulfur