1. Major Clay Minerals Kaolinite – Al 2 Si 2 O 5 (OH) 4 Illite – K 1-1.5 Al 4 (Si,Al) 8 O 20 (OH) 4 Smectites: –Montmorillonite – (Ca, Na) 0.2- 0.4 (Al,Mg,Fe) 2 (Si,Al) 4 O 10 (OH) 2 *nH 2 O –Vermicullite - (Ca, Mg) 0.3- 0.4 (Al,Mg,Fe) 3 (Si,Al) 4 O 10 (OH) 2 *nH 2 O –Swelling clays – can take up extra water in their interlayers and are the major components of bentonite (NOT a mineral, but a mix of different clay minerals)

2. SiO 4 tetrahedra polymerized into 2-D sheets: [Si 2 O 5 ] Apical O’s are unpolymerized and are bonded to other constituents Phyllosilicates

3. Tetrahedral layers are bonded to octahedral layers (OH) pairs are located in center of T rings where no apical O Phyllosilicates

4. Octahedral layers can be understood by analogy with hydroxides Phyllosilicates Brucite: Mg(OH) 2 Layers of octahedral Mg in coordination with (OH) Large spacing along c due to weak van der waals bonds c

5. Phyllosilicates Gibbsite: Al(OH) 3 Layers of octahedral Al in coordination with (OH) Al 3+ means that only 2/3 of the VI sites may be occupied for charge-balance reasons Brucite-type layers may be called trioctahedral and gibbsite-type dioctahedral a1a1a1a1 a2a2a2a2

7. Phyllosilicates Kaolinite: Al 2 [Si 2 O 5 ] (OH) 4 T-layers and diocathedral (Al 3+ ) layers (OH) at center of T-rings and fill base of VI layer  Yellow = (OH) TO-TO-TOTO-TO-TOTO-TO-TOTO-TO-TO vdw vdw weak van der Waals bonds between T-O groups

8. Phyllosilicates Serpentine: Mg 3 [Si 2 O 5 ] (OH) 4 T-layers and triocathedral (Mg 2+ ) layers (OH) at center of T-rings and fill base of VI layer  Yellow = (OH) TO-TO-TOTO-TO-TOTO-TO-TOTO-TO-TO vdw vdw weak van der Waals bonds between T-O groups

9. Clay building blocks Kaolinite micelles attached with H bonds – many H bonds aggregately strong, do not expend or swell 1:1 Clay

10. Clay building blocks 2:1 Clay Slightly different way to deal with charge on the octahedral layer – put an opposite tetrahedral sheet on it… Now, how can we put these building blocks together…

11. Calcite vs. Dolomite dolomite less reactive with HCl calcite has lower indices of refraction calcite more commonly twinned dolomite more commonly euhedral calcite commonly colourless dolomite may be cloudy or stained by iron oxide Mg  spectroscopic techniques! Different symmetry  cleavage same, but easily distinguished by XRD

12. Calcite Group Variety of minerals varying by cation Ca  Calcite Fe  Siderite Mn  Rhodochrosite Zn  Smithsonite Mg  Magnesite

13. Dolomite Group Similar structure to calcite, but Ca ions are in alternating layers from Mg, Fe, Mn, Zn Ca(Mg, Fe, Mn, Zn)(CO 3 ) 2 –Ca  Dolomite –Fe  Ankerite –Mn  Kutnahorite

14. Aragonite Group Polymorph of calcite, but the structure can incorporate some other, larger, metals more easily (Pb, Ba, Sr) –Ca  Aragonite –Pb  cerrusite –Sr  Strontianite –Ba  Witherite Aragonite LESS stable than calcite, but common in biological material (shells….)

15. Carbonate Minerals Calcite Group Calcite Group (hexagonal) Dolomite Group Dolomite Group (hexagonal) AragoniteGroup AragoniteGroup (orthorhombic) mineralformulamineralformulamineralformula CalciteCaCO 3 DolomiteCaMg(CO 3 ) 2 AragoniteCaCO 3 MagnesiteMgCO 3 Ankerite Ca(Mg,Fe)( CO 3 ) 2 WitheriteBaCO 3 Siderite,FeCO 3 KutnohoriteCaMn(CO 3 ) 2 StrontianiteSrCO 3 Rhodochros ite MnCO 3

16. Carbonate Minerals MgFe Ca Calcite, CaCO 3 Dolomite CaMg(CO 3 ) 2 Ankerite CaFe(CO 3 ) 2 Siderite, FeCO 3 Magnesite, MgCO 3

17. Sulfate Minerals More than 100 different minerals, separated into hydrous (with H 2 O) or anhydrous (without H 2 O) groups Gypsum (CaSO 4 *2H 2 O) and anhydrite (CaSO 4 ) are the most common of the sulfate minerals Gypsum typically forms in evaporitic basins – a polymorph of anhydrite (  -CaSO4) forms when the gypsum is later dehydrated)

18. Gypsum

19. Gypsum formation can demarcate ancient seas that dried up (such as the inland seas of the Michigan basin) or tell us about the history of current seas which have dried up before (such as the Mediterranean Sea)

20. Halide Minerals Minerals contianing halogen elements as dominant anion (Cl - or F - typically) Halite (NaCl) and Sylvite (KCl) form in VERY concentrated evaporitic waters – they are extremely soluble in water, indicate more complete evaporation than does gypsum Fluorite (CaF 2 ) more typically occurs in veins associated with hydrothermal waters (F - in hydrothermal solutions is typically much higher – leached out of parent minerals such as biotites, pyroxenes, hornblendes or apatite)

21. Halite Structure NaCl  Na + (gray) arranged in CCP with Cl - (red) at edges and center (in octahedral cavities)

22. Flourite structure CaF 2  Ca 2+ (gray) arranged in CCP, F- ions (red) inside ‘cage’

23. Sulfate Minerals II Barite (BaSO 4 ), Celestite (SrSO 4 ), and Anglesite (PbSO 4 ) are also important in mining. These minerals are DENSE  Barite =4.5, Anglesite = 6.3 (feldspars are ~2.5)

24. Barite, Celestite, Anglesite Metals bond with sulfate much more easily, and thus are generally more insoluble – they do not require formation in evaporitic basins What do they indicate then? Ba, Pb, Sr – very low SO 4 2- Lots of SO 4 2- Not very much Ba, Sr, Pb

25. Just silica… Chert – extremely fine grained quartz –Forms as nodules in limestone, recrystallization of siliceous fossils –Jasper – variety with hematite inclusions  red –Flint – variety containing organic matter  darker color Chalcedony – microcrystaliine silica (very similar to low quartz, but different – it is yet uncertain how different…)  typically shows banding, often colored to form an agate (rock formed of multiple bands of colored chalcedony) Jasper – variety colored with inclusion of microcrystsalline oxides (often iron oxides = red) Opal – a hydrogel (a solid solution of water in silica) – forms initially as water + silica colloids, then slowly the water diffuses into the silica  making it amorphous (no XRD pattern!) –Some evidence opal slowly recrystallizes to chalcedony

26. Opal - Gemstone

27. Agates

28. Oxides - Oxyhydroxides FeOOH minerals  Goethite or Limonite (FeOOH)  important alteration products of weathering Fe-bearing minerals Hematite (Fe 2 O 3 )  primary iron oxide in Banded Iron Formations Boehmite (AlOOH)  primary mineral in bauxite ores (principle Al ore) which forms in tropical soils Mn oxides  form Mn nodules in the oceans (estimated they cover 10-30% of the deep Pacific floor) Many other oxides important in metamorphic rocks…

30. Mn oxides - oxyhydroxides Mn exists as 2+, 3+, and 4+; oxide minerals are varied, complex, and hard to ID –‘Wad’  soft (i.e. blackens your fingers), brown-black fine-grained Mn oxides –‘Psilomelane’  hard (does not blacked fingers) gray- black botroyoidal, massive Mn oxides XRD analyses do not easily distinguish different minerals, must combine with TEM, SEM, IR spectroscopy, and microprobe work

31. Romanechite Ba.66 (Mn 4+,Mn 3+ ) 5 O 10 *1.34H 2 O  Psilomelane Pyrolusite MnO2 Ramsdellite MnO2 Nsutite Mn(O,OH)2 Hollandite Bax(Mn4+,Mn3+)8O16 Cryptomelane Kx(Mn4+,Mn3+)8O16 Manjiroite Nax(Mn4+,Mn3+)8O16 Coronadite Pbx(Mn4+,Mn3+)8O16 Todorokite (Ca,Na,K)X(Mn4+,Mn3+)6O12*3.5H2O Lithiophorite LiAl2(Mn2+Mn3+)O6(OH)6 Chalcophanite ZnMn3O7*3H2O Birnessite (Na,Ca)Mn7O14*2.8H2O Vernadite MnO2*nH2O Manganite MnOOH Groutite MnOOH Feitknechtite MnOOH Hausmannite Mn 2+ Mn 2 3+ O4 Bixbyite Mn2O3 Pyrochroite Mn(OH)2 Manganosite MnO Mn Oxide minerals (not all…) Wad

32. Iron Oxides Interaction of dissolved iron with oxygen yields iron oxide and iron oxyhyroxide minerals 1 st thing precipitated  amorphous or extremely fine grained (nanocrystaliine) iron oxides called ferrihydrite Fe 2+ O2O2

33. Ferrihydrite Ferrihydrite (Fe 5 O 7 OH*H 2 O; Fe 10 O 15 *9H 2 O  some argument about exact formula) – a mixed valence iron oxide with OH and water

34. Goethite Ferrihydrite recrystallizes into Goethite (  - FeOOH) There are other polymorphs of iron oxyhydroxides: –Lepidocrocite  -FeOOH –Akaganeite  -FeOOH

35. Iron Oxides Hematite (Fe 2 O 3 ) – can form directly or via ferrihydrite  goethite  hematite Red-brown mineral is very common in soils and weathering iron-bearing rocks

36. Magnetite (Fe 3 O 4 ) – Magnetic mineral of mixed valence  must contain both Fe 2+ and Fe 3+  how many of each?? ‘Spinel’ structure – 2/3 of the cation sites are octahedral, 1/3 are tetrahedral

37. Banded Iron Formations (BIFs) HUGE PreCambrian formations composed of hematite-jasper-chalcedony bands Account for ~90% of the world’s iron supply Occur only between 1.9 and 3.8 Ga  many sites around the world  Hammersley in Australia, Ishpeming in Michigan, Isua in Greenland, Carajas in Brazil, many other sites around the world…