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Minerals. Chapter 3. Minerals known to ancient peoples. Crystalline Structure. Chemistry within limits Internal Structure within limits Permits identification based on chemical and physical properties. Minerals are orderly crystalline structures. Helium Atomic Number 2 Atomic Weight 4.
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Minerals Chapter 3
Crystalline Structure • Chemistry within limits • Internal Structure within limits • Permits identification based on chemical and physical properties
Helium Atomic Number 2 Atomic Weight 4 Neon Atomic Number 10 Atomic Weight 20
Atoms Same number of protons and electrons No charge Inert Ions Gain or loose electrons to fill outer electron shell Charged Larger or smaller than atom Atoms and Ions
Anion Gains electrons Negative charge Larger that atom Cation Loose electrons Positive charge Smaller than atom Metals Ions
8 most abundant elements in the Earth’s crust • Element Symbol Charge Size Atom Size Ion • Oxygen O - - 0.60 1.40 • Silicon Si ++++ 1.17 0.42 • Aluminum Al +++ 1.43 0.51 • Iron Fe ++ (+++) 1.24 0.74 • Calcium Ca ++ 1.96 0.99 • Sodium Na + 1.86 0.97 • Potassium K + 2.31 1.33 • Magnesium Mg ++ 1.60 0.66
Organization of ions into a crystal lattice • Sizes of ions • Charges of ions • Unit Cell is the smallest assemblage of ions that satisfies both ionic sizes and charges • The unit cell is much larger the simple chemical formula
Coordination • Radius Ratio Coordination Number 1.000 12 0.999 - 0.732 8 0.731 – 0.414 6 0.413 – 0.225 4 0.224 – 0.115 3 <0.114 2
Coordination • Coordination is controlled by the relative sizes of ions • Radius ratio is Radius of Cation divided by Radius of Anion • Limits 0.01 and 1.00
Example • Na cation 0.97 • Cl anion 1.81 • Radius Ratio 0.54 • Coordination Number 6 • Can fit 6 sodium ions around a chlorine ion • Conversely there are 6 chlorine ions around a sodium ion
Next balance the charges • 6 Na at -1 = -6 • 6 Cl at +1 = +6 • Net charge = 0
Oxygen and Silicon • O ionic radius 1.40 -2 • Si ionic radius 0.42 +4 • Radius Ratio 0.3 • Coordination Number 4 • 4 O -2 = -8 • 1 Si +4 = +4 • Net Charge -4
Silicate Tetrahedron • Stick Model Cell Model Schematic
Mineral Classes(Simple) • Elements (12 fold coordination) • Oxides (4 and 6 fold coordination) • Sulfides (6 fold coordination) • Halides (6 fold coordination)
Mineral ClassesCompound • Carbonates (CO3) -2 2.95 3 fold • Sulfates (SO4) -2 3.08 3 fold • Silicates (SiO4 ) -4 3.20 4 fold
Unit Cell • Controls crystal form • Controls cleavage • Controls fracture • Revealed by striations on crystal and cleavage faces
Crystallization from melt (Plutonists) • Igenous • Precipitation from water (Neptunists) • Sediment • Transformation of organic materials • Sediment • Chemical transformation from previous minerals • metamorphism
Assignment • Chapter 4 Igneous Rocks • Important terms • Magma • Texture • Bowen’s reaction series • Crystallization – Melting