Lecture 5 Minerals and SilicatesOutline QuestionsContined from last timeCompounds – bonded elementsIons and Atomic radiiSlide 6Slide 7Polymorphs: Minerals that have the same formula but different crystal structureComplex Ions (radicals)Slide 10Slide 11Slide 12Classification of mineralsSlide 14Slide 15Slide 16Slide 17Slide 18Slide 19Remember….Slide 21Mineral propertiesPhysical properties of MineralsSlide 24Slide 25Slide 26Slide 27Complex Ions (radicals) The silica-oxygen tetrahedral SiO4Slide 29Slide 30The SiO4 Tetrahedral can be represented in many ways:Because the SiO4 still has a 4- charge, it can bond to other silica tetrahedrals, and a variety of CationsSlide 33Slide 34Various Cations can bond with silicatesSometimes various cations may substitute for one anotherSlide 37Rock-Forming MineralsFerromag Minerals MAFICSlide 40Sialic Minerals FELSICSlide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Lecture 5Minerals and SilicatesOutline QuestionsWhat are compounds?Why are complex ions importantWhat are the Mineral groups?Describe the Physical properties of mineralsWhat is the silica tetrahedral and why is it important?Contined from last time•Bonded elements = Compounds!Compounds – bonded elements•Compounds, then are:–Often neutral in overall charge•If existing as a solid, compounds have–Geometric “packing”–Exhibit “closest packing” (determined by the prevailing energy conditions during mineral formation)How do the atoms arrange themselves?By Size and ChargeIons and Atomic radii•Atomic radii–The distance from the center of nucleus to the outer electron shell–i.e. the “size” of an atom•Cations v Anions–Which is larger and why?•Cations lose electrons; Anions gain electrons•Size also determined by atomic number, the more Protons and Neutrons, then, the larger the atomNaClHALITECaCO3CALCITECrystal structure is a repeating geometric sequence beginning at the micro scale and continuing to macro scalePolymorphs: Minerals that have the same formula but different crystal structureComplex Ions (radicals)•In some cases, covalently bonded compounds can still retain a charge•Example: Carbon can give up 4 electrons to empty its half-filled shell•Results in C4+ Ion•Oxygen can gain 2 electrons to fill shell•Results in O2- Ion•Thus, one C4+ atom can covalently bond with two O2- atoms to form the electrically neutral CO2 compoundComplex Ions (radicals)•However, at other times, the C4+ may actually bond with 3 O2-, thus the overall compound is: CO3 which has a 2- charge. It is depicted as (CO3)2- and these charged compounds are known as a Complex Ion or Radical•(CO3)2- is called Carbonate and will bond with other cations such as Ca2+ to form CaCO3 which as a mineral is known as Calcite. It could also bond with Fe3+ to form the mineral Siderite.Complex Ions (radicals)•Silicon and Oxygen can also form a complex ion. Si4+ can bond with 4 O2- to make the SiO4 ion (called silica). •(SiO4)4- can bond with a variety of cations or combinations of cations to make many different compounds/minerals•Highly important – Si and O are the two most common elements in earth’s crust (Al is #3) and thus form the basis for the majority of minerals and rocks!•More discussion on silicate minerals laterClassification of minerals•Minerals are classified by their Anions or Anionic radical group (except native elements)1. Native elementsNative elements – Au, Ag, Cu, Diamond (C), etc.Classification of minerals2. OxidesOxides: Cations combine with oxygen (valence of –2)Hematite Iron Oxide Fe2O3MagnetiteIron oxideFe3O4Rubies and SapphiresAluminum oxideAl2O3Classification of minerals3. SulfidesSulfides: Cations combine with sulfur (valence of –2)Pyriteiron sulfideFeS2Galenalead sulfidePbSClassification of minerals4.4.HalidesHalides: Cations combine with anions that have a valence of –1 (chlorine, fluorine, bromine, etc.)Halitesodium chlorideNaClFluoritecalcium fluorideCaF2Classification of minerals5. CarbonatesCarbonates: Cations combine with the (CO3)-2 unitCalcitecalcium carbonateCaCO3Dolomitemagnesium carbonateCa, Mg(CO3)Gypsumcalcium sulfateCa(SO4)Classification of minerals6. SulfatesSulfates: Cations combine with a negatively charged unit that consists of 1 sulfur and 4 oxygen ions (SO4)-2Classification of minerals7. SilicatesSilicates: Cations combine with a unit that consists of 1 silicon and 4 oxygen ions (SiO4)-4Quartz (SiO2)Collectively, silicates comprise about 1/3 of all mineral speciesSilicate minerals account for about 95% of the volume of the Earth’s crust and are the “Rock-forming” mineralsTogether, oxygen (O) and silicon (Si) make up about 75% of the Earth’s crustRemember….•A mineral is:“Naturally occurring, inorganic solid with a specific chemical formula and definite crystal structure”NaClHALITECaCO3CALCITECrystal structure is a repeating geometric sequence beginning at the micro scale and continuing to macro scaleMineral properties•Determined by Chemistry and/or Crystal structurePhysical properties of Minerals•Luster – how it reflects light•Color – not very diagnostic in many cases•Streak – color of powdered residue•Cleavage – preferred planes of weakness–Bonds!•Hardness – resistance to scratching•Special properties – taste, smell, magnetism, effervescenceColor (?)Luster: the appearance of a mineral in reflected lightStreak: the color of the powdered mineralCleavage: the tendency to break along parallel planesSpecial properties: effervescence, magnetism, fluorescence, taste, smellComplex Ions (radicals)The silica-oxygen tetrahedralSiO4Silicate minerals7. SilicatesSilicates: Cations combine with a unit that consists of 1 silicon and 4 oxygen ions (SiO4)-4Quartz (SiO2)Collectively, silicates comprise about 1/3 of all mineral speciesSilicate minerals account for about 95% of the volume of the Earth’s crust and are the “Rock-forming” mineralsTogether, oxygen (O) and silicon (Si) make up about 75% of the Earth’s crustThe basic building block of all silicate minerals is the silicon-oxygen tetrahedron4 oxygen ions, each with a valence of -2 (4 X –2 = -8)The structure of the (SiO4)-4 unit is a function of the radii (or size) of the ions1 silicon ion, with a valence of +4 (1 X +4 = +4)-4The SiO4 Tetrahedral can be represented in many ways:Imagine a tennis ball surrounded by 4 volleyballsBecause the SiO4 still has a 4- charge, it can