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Planet earth minerals_powerpoint_presentation Presentation Transcript

  • 1. Matter and MineralsThe spectacularscenery of theSierra NevadaMountains inCalifornia resultsfrom glaciersthat carved highpeaks and deepvalleys into amassive body ofgranite -- acommon type ofigneous rock.Igneous rocksare rocks thatform the coolingand solidificationof molten magma. 1
  • 2. Summary of Important Concepts to Be Covered• The Earth consists of four interconnected systems: the solid earth or lithosphere (rock and soil); the atmosphere; the hydrosphere; the biosphere; These systems interact and influence each other.• The earth’s crust consists of rocks made of various types of minerals. Minerals are classified into different groups according to their chemistry. The silicate mineral group makes up most rock of the crust. 2
  • 3. Summary of Important Concepts to Be Covered• Rocks are composed on one or more minerals. There are three main classes of rocks: – Igneous rocks form from solidification of magma (molten rock) – Sedimentary rocks form from solidification of sediment (particles formed from the erosion of older rocks, or by chemical or biological processes at the earth’s surface). – Metamorphic rocks form from other rocks changed by heat and pressure• One type of rock can be transformed into another type over geologic time; a process known as the rock cycle. 3
  • 4. The earth’s crust ismade of variouskinds of rock, androck is composed ofone or moreminerals. Forexample, as thispicture shows, therock granite iscomposed mostly ofthe minerals quartz,biotite, andfeldspar. 4
  • 5. Importance of Minerals• Knowing the chemistry is essential to knowing how they combine to form rocks and the stability of the rocks.• Uses: natural resources, nutrients, metals, building materials, jewelry, computer chips.• ~4000 species of mineral but only about 20 or so are actually common. 5
  • 6. Definition of a Mineral• Naturally occurring (not synthesized by man).• Inorganic (not made from living organisms).• Solid that is homogenous (the same throughout).• Ordered crystalline structure (atoms are arranged in a definite pattern that repeats throughout the entire mineral).• Definite chemical composition expressed with a formula. Halite or common table salt NaCl 6
  • 7. Atoms, atoms, atoms!• An element is electrically neutral.• ~92 naturally occurring, ~17 man made• Smallest unit of matter that cannot be broken down into other substances (i.e. it’s the smallest part of the element that retains the properties of that element). 7
  • 8. Periodic Table of the Elements http://www.chemicalelements.com 8
  • 9. Minerals are made of variouschemical elements, or atoms.Atoms, which form all matter,consist of three kinds of particles.-- protons with a positive chargeand neutrons with a neutral charge-- occupy the center, or nucleus,of the atom. The nucleus containsnearly all the mass of the atom.-- electrons with a negative charge-- orbit around the nucleus.Electrons have almost zero mass.All atoms have this same generalstructure. By changing thenumbers of protons we makedifferent chemical elements! 9
  • 10. Periodic Table of the Elements 10
  • 11. Anatomy of an Atom • Atomic number = # of protons (+). Determines the element. • Atomic mass= # protons and neutrons in nucleus. • Neutrons, no charge, contributes to atomic mass. • Electrons (-), doesn’t contribute to mass. • All atoms are electrically neutral. That means the number of protons (+) in the nucleus eguals the number of electrons orbiting the nucleus. 11
  • 12. • Negatively charged sub-atomic particles that move very quickly around the nucleus. Electrons• Electrons are arranged in ‘shells’ or ‘orbitals’ around the nucleus. Electron shells are merely SPACE surrounding the nucleus at different levels. Electrons within a shell can move anywhere within this space.• The shells are layered where the first shell can only hold up to two electrons. Each successive shell can hold up to 8 (as you get up in atomic number, the number or electrons/shell varies…we will not worry about that).• For an atom to be STABLE, that is, not ‘bond’ or chemically react with another atom, its VALENCE shell (outermost shell) must be full.• Electrons and valence shells are involved in chemical BONDING. 12
  • 13. Chemical bonding betweenelements forms minerals. Covalent and Ionic Bonds 13
  • 14. TO BOND OR NOT TO BOND• If the number of protons equals the number of electrons (+ = -) and the ‘checkbook’ balancesthe atom has no charge.• Having no charge does not necessarily mean the atom is stable.• Take Na (sodium). Check the periodic table to get its atomic number (the number of protons, that is). 14
  • 15. TO BOND OR NOT TO BOND• Na atomic number is 11.• How many electrons in the valence shell?• One valence electron. Well to be stable and non reactive, we want to have a full valence shell.• Na can accept 7 electrons or give up 1. Which seems easier? 15
  • 16. TO BOND OR NOT TO BOND• Sure! It is much easier to donate that one electron so that the shell is full.• What is the charge on sodium if it gives up that electron?• +1 It has a plus one charge and is now called an ION, specifically a cation (positively charged ion).• Diagram shows sodium atom on the left and the ion on the right. Sorry, its in french.• If an element gives away two electrons it will have a +2 charge and so forth and so on. 16
  • 17. TO BOND OR NOT TO BOND• Now go look up the atomic number for Chlorine Cl. How about the valence shell?• You should come up with 7 valence electrons. What a dilemma. Cl only needs ONE more electron to have a full valence shell.• If Cl obtains one electron it will have 17 protons, 18 electrons and a charge of -1. An anion is a negatively charged ion.• Now we have an electric glue. Opposites attract right? Well, Na+1 and Cl-1 will have to form a bond. 17
  • 18. Ionic Bonds • An ionic bond is the chemical bond that results from the electrostatic attraction between positive ions (cations) and negative ions (anions). It can form when two atoms meet and an electron is permanently transferred from one to the other. These two ionized atoms then stick very tightly together to make sodium chloride -- also known as table salt (or the mineral halite). 18
  • 19. So basicallyelectric glue holds NaCl together. This bond is notthat strong (as we can dissolve NaCl easily in water). For any element, be able to determine the valence electronsand what charge it would have if it would become an ion. 19
  • 20. • Okay so what if you have 4Covalent valence electrons. Would you give up or obtain 4 electrons. Bond Probably neither. Your best bet in this situation is to just SHARE the electrons. • Covalent chemical bonds involve the sharing of a pair of valence electrons by two atoms. A Covalent bond is formed when the valence shells of two atoms overlap and the electrons are free to roam between both shells. • The number of covalent bonds an atom can have depends on the number of valence electrons. 20
  • 21. Covalent Bonding Note: the morecovalent bonding a mineral has in its structure, the more stable (stronger) thatmineral is, and the more difficult toweather or break it down. 21
  • 22. Common Elements of the Earth’s Crust• Okay so if there are thousands of minerals, why only a few common ones? The answer is that there are only a few elements that make up MAJORITY of the earths minerals (and minerals make up rocks).• Si (silicon)• O (oxygen) Si and O form the silica tetrahedron• Na (sodium) +1• K (potassium) +1• Ca (calcium) +2• Mg (magnesium) +2• Al (aluminum)+3• Fe (iron) +2• 98% of the earth’s crust are made of combinations of these 8 elements.• 92% of the earth’s crust are made of ‘silicate’ minerals, those containing mostly Si and O. 22
  • 23. Geologists classify minerals into groups that share the samenegatively charged atoms or molecules.For example:The oxide groupconsists of all mineralsformed from variouselements bonded tonegatively chargedoxygen (O -2) atoms.The carbonate groupconsists of all mineralsformed from elementsbonded to negativelycharged carbonate((CaCO3 ) -2 ) molecules.The silicate mineralsare the MOSTCOMMON minerals inthe earth’s crust. 23
  • 24. feldspar Silicate MineralsThe silicates are the mostabundant and importantmineral group.Silicates are minerals composedof silicate tetrahedra (SiO4)- 4 quartzbonded to each other and/or toother elements. A single silicatetetrahedron consists of 1 silicon hornblende(Si) atom surrounded by 4 oxygen(O) atoms, forming a tetrahedronshape. These tetrahedra bondreadily to each other, and toother elements, forming severalkinds of abundant minerals,including quartz and feldspar. muscovite mica 24
  • 25. The fundamental building The Silica block for the silicate minerals is called the Tetrahedron silica tetrahedron. Stats on Si and O are as follows:Si atomic number is 14How many valence e-? (4)O atomic number is 8How many valence e-? (6)Silicon therefore can form four covalent bonds with oxygen atoms. 25
  • 26. The Silica Tetrahedron 26
  • 27. The Silica Tetrahedron 27
  • 28. The Silica TetrahedronIf each oxygen (four total) share one electron with silicon, then silicon’s valence shell is full, but what about oxygen?No, each oxygen has two ‘vacancies’ in its valence shell and will require two covalent bonds. So now what? 28
  • 29. The Silica Tetrahedron• The chemical formula Si04 will then have a net negative 4 charge. This is because, each of four oxygens have one vacancy in their valence shells. Each Oxygen therefore needs to obtain one more electron to fill its outer shell.• If the MOLECULE accepts four electrons to become STABLE (and it will), the tetrahedron itself will have obtained four electrons (have full valence shells) and will have an overall charge of -4. 29
  • 30. So where does it get these other 4 electrons? From atoms that want to get rid of their valence electrons (to become cations).Of the remaining abundant elements of the earth’s crust, you can see that thereare many combinations of cations (bottom right) that will form ionic bonds to the tetrahedron and thus form a variety of different minerals. So, eight elements can make many different SILICATE minerals that make up the earth’s crust. 30
  • 31. The Silica Tetrahedron 31
  • 32. The silica tetrahedron itself is covalently (strong) bound, but each tetrahedra iselectrically glued to adjacent tetrahedra via the cations. If the ‘silica tetrahedrabackbone’ is arranged in this way, we call this the isolated silicate structure (see next slide). The OTHER way the silica tetrahedra can‘fill’ its valence shells is by covalently bonding to adjacent tetrahedra. If it forms two, three, or four covalent bonds (oxygens sharing electrons with oxgyens of adjacent tetrahedra) and subsequent demand for electrons drops, the net negative charge on the tetrahedron becomes less and less. If all four oxygens share electrons, allcovalent bonds are formed. There will be no charge (and thus no bonding to cations). 32
  • 33. The figure shows the shape of the silicate tetrahedron, and showshow progressively more complex bonding between silicatetetrahedra forms the different types of common silicate minerals. 33
  • 34. Isolated Silicate Minerals • Olivine is an example. • Consists of one tetrahedron bound by 4+ ions. • It is ‘isolated’ because it shares no oxygen atoms with other tetrahedra. • Si:O = 1:4 = +4:-8, net charge = -4 • -4 binds to +4 cations. • Because this silicate structure has the highest negative charge, it will form the MOST amount of ionic bonds with adjacent tetrahedra rendering this the WEAKEST silicate structure. • Olivine contains a lot of Fe and Mg (recall layers of the earth and distribution of Fe, Mg, Si and O). 34
  • 35. Single Chain Silicates • Augite is an example. • Look at the diagram to the left A-single chains. • View a single blue dot representing the silicon atom— each is surrounded by four beige oxygen atoms. • Pick out any tetrahedra and see how TWO oxygens are being shared with adjacent tetrahedra. • Because of some covalent bonding in this ‘backbone’ the net charge is -2 for this structure. • Per individual tetrahedra, only two electrons are accepted for the two NON covalently bound oxygens. • The demand for + ions is less. These minerals have more covalent bonds than the isolated structure and are subsequently stronger. 35
  • 36. Double Chain Silicates •Hornblende is an example. •Examine the B-Double silicate in the figure. Every other tetrahedron shares 3 OR 2 oxygens. •These silicates have MORE covalent bonds and LESS ionic bonds than the single chains (and so are stronger yet). •Si:O = 1:2.75 •+4:-5.5, net charge –1.5 •Double chains of silicates are linked together by +1.5 ‘worth’ of cations. 36
  • 37. SheetSilicates•Muscovite and Biotite asexamples.•Suppose we covalently bindthree oxygens with adjacenttetrahedra. The only oxygen thathad accepted an electron is thetop oxgyen (see diagram—it isthe one pointed at you).•The silica is arranged in sheets,and the sheets are electricallyglued together by cations. Theseminerals break easily betweenthe ionic bonds between thesheets.•Si:O = 1-2.5•+4:-5, net charge –1•Positive ions IONICALLY bondsheets together. 37
  • 38. Framework Silicates Each tetrahedron shares all four oxygens with adjacent tetrahedra. Si:O = 1:2. All four oxygens shared with adjacent tetrahedron forms a complex 3-D network, all covalently bound. Quartz as an example. Quartz therefore is a pretty stable mineral as it is only SiO2 all covalently bound. The reason that the formula is SiO2 is because each silicon ‘owns’ half of four oxygens (sharing with other silicon atoms). Quartz (and glass) will not ‘break’ in a straight line or preferential direction (minerals tend to break along planes of weakness resulting from ionic bonds). Four covalent bonds means strength between the atoms is equal in all directions. Hence, glass (and quartz) breaks in curved patterns (wherever the force was the strongest). 38
  • 39. Silicate Isolated Single Chain Double Chain Sheet Framework Structure Example Olivine Augite Hornblende Mica Quartz Percent SiO2 Lowest Lower Low Medium High Highest Higher High Medium LowPercent Fe, Mg Ultramafic Mafic Mafic Felsic Felsic Si:O 1:4 1:3 1:2.75 1:2.5 1:2 Net Charge +4-8=-4 +4-6=-2 +4-5.5=-1.5 +4-5=-1 +4-4=0Covalent Bonds Lowest Lower Low Medium High Ionic Bonds Highest Higher High Medium Low Density Highest Higher High Medium Low Stability Lowest Lower Low Medium High 39
  • 40. Felsic Silicate MineralsOf the Silicates we can divide them up into smaller groups.FELSIC silicate minerals contain high percentages of Si and O and very little Fe and Mg (sometimes none at all).Examples include Quartz, Orthoclase Feldspar, Plagioclase Feldspar.Felsic minerals ‘tend’ to be light colored.What layer of the earth do you think would be made up of rock composed of felsic minerals?Answer: CONTINENTAL 40 CRUST
  • 41. Of the silicates, those that have higher percentages of Mafic Silicate Fe and Mg are called MAFIC minerals. MineralsThey tend to be darker in color.Examples include Olivine, Hornblende, Augite, Biotite Mica.Mafic minerals, due to their higher percentages of iron and magnesium means they are ‘heavier’ or denser.Which layers of the earth should have the denser stuff?Answer: OCEANIC CRUST 41
  • 42. Non-Silicate Minerals do not have the silica tetrahedron. • Any minerals that do NOT contain silica in their chemical formula. • Examples, Halite (NaCl), Fluorite (CaF2), Calcite (CaCO3), Magnetite (Fe3O4). 42
  • 43. Non-Silicates Metallic minerals include: Al (3rd most common element) Cu copper electrical Pb lead batteries Zn zinc coats ‘tin’ cans Au, Ag, Pt 43
  • 44. Mineral IdentificationMinerals take the formof crystals of differentcolors and shapes.The different colorsresult from the ways thatdifferent atoms absorband reflect light.The different shapesresult from the differentways that bonded atomspack together inparticular geometricarrangements. 44
  • 45. Mineral IdentificationFracture and CleavageThese terms describethe way a mineralbreaks. If a mineralfractures, it breaksalong rough edges. Ifit cleaves, then itbreaks along smooth,flat surfaces ordefinite planes asdetermined by theircrystal structure. 45
  • 46. MineralIdentificationTypes of Cleavage andtypical minerals inwhich they occur.Note: quartz iscovalent bonds(framework silicate)equal in all directions.Quartz does not breakin a preferentialdirection or plane so itdoesn’t have cleavage.It has fracture(breaks any which way). 46
  • 47. Mineral IdentificationThis Biotitecleaves into flatsheets on the top,but it fractures onthe sides. When some minerals fracture, they appear to break along long curved surfaces (that look like a shell) like that shown left. 47
  • 48. Mineral IdentificationHardness Mohs hardness scaleThis is how resistant a mineralis to being scratched. We use TALC 1the Mohs scale to classify a GYPSUM 2given minerals hardness. CALCITE 3 FLUORITE 4The technique is rather simple. All you do istry to scratch the unknown mineral with APATITE 5minerals of the mohs hardness scale or FELDSPAR 6various items of known hardness, such as a QUARTZ 7fingernail (hardness of about 2.5), a penny TOPAZ 8(3), and a steel nail (5.5). The item that CORUNDUM 9first scratches the unknown is harder thanthe unknown so then you must estimate. DIAMOND 10 48
  • 49. Mineral IdentificationLuster The way a mineral reflects light. Luster can be metallic - looks like a metal; or nonmetallic. Nonmetallic minerals can be described with other terms such as glassy, oily, greasy, and earthy. 49
  • 50. Mineral Identification The color of a mineral when itStreak is powdered is called the streak of the mineral. Streak can be determined for any mineral by rubbing the mineral across the surface of a hard, unglazed porcelain material called a streak plate. The color of the powder left behind on the streak plate is the minerals streak. 50
  • 51. Mineral Chemistry• So the take home message is that mineral chemistry determines the ‘strength of the mineral’ and contributes to the mineral’s properties.• The more covalent bonding a mineral has, the less the ionic bonding and the stronger it is.• Minerals with higher percentages of iron and magnesium (and therefore a lot of ionic bonds) have weaker silicate structures (isolated, single, double) and are denser. These minerals make up denser layers of the earth.• Minerals with lower percentages of iron and magnesium (due to more covalent bonding between adjacent tetrahedra) have stronger silicate structures (sheet, framework) and are lower density.• We will DEFINITELY revisit this stuff during igneous rocks, metamorphic rocks, weathering, etc. 51