1 Structure of Minerals 2 Structure of minerals } An orderly array of atoms chemically bonded to form a particular crystalline structure 3 Structure of minerals } An orderly array of atoms chemically bonded to form a particular crystalline structure } Arrangement primarily determined by the sizes of ions 4 Relative Sizes of Common Elements 5 Ideal Geometric Packing for Various-sized Ions 6 Ideal Geometric Packing for Various-sized Ions } Each cation surrounded by the largest number of anions that will fit. 7 The Orderly Arrangement of Sodium and Chloride Ions Is Reflected in the Cubic Shape of the Halite Crystal 8 Def: Polymorphs } Different minerals with the same chemical composition but different crystalline structures 9 Def: Polymorphs Graphite, diamond, and buckminsterfullerene are all made of Carbon! 10 Diamond and graphite: polymorphs of C 11 Classification of Minerals } Nearly 4000 minerals have been identified on Earth! 12 Classification of Minerals } Nearly 4000 minerals have been identified on Earth! } Rock-forming minerals ÑMake up most of Earth’s crust ÑOnly a few dozen ÑComposed mainly of the 8 common elements 13 14 Silicon-oxygen tetrahedron – the silicate building block 15 How do the silicon-oxygen tetrahedra balance their 1 charges? }By bonding with positive ions 16 How do the silicon-oxygen tetrahedra balance their charges? }By bonding with positive ions }By sharing their oxygen ions to form structures 17 Classification of Minerals } Silicate structures ß Isolated tetrahedra ß Single chain structures ß Double chain structures 18 Classification of Minerals } Silicate structures, cont. ß Sheet or layered structure ß Complex 3-dimensional structures 19 Single, double chain, and sheet structures 20 Def.: Solid Solutions } Some ions can SUBSTITUTE for other similar sized and charged ions } Ex: (Fe,Mg)2SiO4 21 Five mineral groups account for 90% of all of the Earth’s crust }Feldspar }Quartz }Pyroxene }Amphibole 2 }Mica 22 Feldspar, Quartz, Hornblende (amphibole) 23 Mica 24 25 Common silicate minerals ÑOlivine ß High temperature ß Individual silicate tetrahedra linked by Fe and Mg ß Small, rounded crystals with no cleavage 26 Olivine 27 Common Silicate minerals ÑPyroxene Group ß Single chain structures involving Fe and Mg ß Two distinctive cleavages at nearly 90 degrees ß Augite is the most common mineral in the pyroxene group 28 Common Silicate minerals ÑAmphibole Group ß Double chain structures involving a variety of ions ß Two perfect cleavages exhibiting angles of 124 and 56 degrees ß Hornblende is the most common mineral in the amphibole group 29 Cleavage angle for augite and hornblende 30 Hornblende crystals 31 Microscopic hornblende crystal 32 Common Silicate minerals ÑMica Group ß Sheet structures that result in one direction of perfect cleavage ß Biotite is the common dark colored mica mineral ß Muscovite is the common light colored mica mineral 3 33 Name? 34 Common Silicate minerals ÑFeldspar Group ß Most common mineral group ß 3-dimensional framework of tetrahedra exhibit two directions of perfect cleavage at 90 degrees ß Orthoclase (potassium feldspar) and Plagioclase (sodium and calcium feldspar) are the two most common members 35 Potassium feldspar 36 Plagioclase feldspar 37 Common silicate minerals ÑClay minerals ß Clay is a general term used to describe a variety of complex minerals ß Clay minerals all have a sheet or layered structure ß Most originate as products of chemical weathering 38 Clay mineral structure 39 Important nonsilicate minerals 40 41 Oxide - Hematite 42 43 Sulfide – name? 44 Sulfide – name? 45 46 Native element – name? 47 Native element –name? 48 49 Halide –name? 50 51 Important nonsilicate minerals }Carbonates 4 ß Primary constituents in limestone and dolostone ß Calcite (calcium carbonate) and Dolomite (calcium- magnesium carbonate) are the two most important carbonate minerals 52 Carbonate - Calcite 53 Important nonsilicate minerals ÑMany nonsilicate minerals have economic value ÑExamples ß Hematite (oxide mined for iron ore) ß Halite (halide mined for salt) ß Sphalerite (sulfide mined for zinc ore) ß Native Copper (native element mined for copper) 54 Native Copper 55 End of Chapter 2 5.