1. What happens when granite is weathered??
First, unweathered granite contains these minerals:
Na Plagioclase feldspar
K feldspar
Quartz
Lesser amounts of biotite, amphibole, or muscovite
What happens when granite is weathered?
The feldspars will undergo hydrolysis to form kaolinite (clay) and Na and K ions
The Na+ and K+ ions will be removed through leaching
The biotite and/or amphibole will undergo hydrolysis to form clay, and oxidation to form iron oxides.

2. Granite weathering, continued
The quartz (and muscovite, if present) will remain as residual minerals because they are very resistant to weathering.
Weathered rock is called saprolite.
What happens after this?
Quartz grains may be eroded, becoming sediment. The quartz in granite is sand- sized; it becomes quartz sand. The quartz sand will ultimately be transported to the sea (bed load), where it accumulates to form beaches.
Clays will ultimately be eroded and washed out to sea. Clay is fine-grained and remains suspended in the water column (suspended load); it may be deposited in quiet water.
Dissolved ions will be transported by rivers to the sea (dissolved load), and will become part of the salts in the sea.

3. Sedimentary Minerals
We will focus on some minerals which form from precipitation of dissolved ions  other minerals in sedimentary rocks are derived from the source rocks!
Clay, carbonate, and sulfate groups are key in sedimentary rocks – can ‘be’ the rock or cement fragments together!
SiO44-, CO32-, SO42- anionic groups, respectively
Also consider halides (anion is Cl- or F-) and mineralization of silica

4. Sheet Silicates – aka Phyllosilicates
Clays
Sheet Silicates – aka Phyllosilicates
[Si2O5] Sheets of tetrahedra Phyllosilicates
micas talc clay minerals serpentine

5. Sheet Silicates – aka Phyllosilicates
[Si2O5] Sheets of tetrahedra Phyllosilicates
micas talc clay minerals serpentine
Clays  talc  pyrophyllite  micas
Display increasing order and lower variability of chemistry as T of formation increases

6. Clays Term clay ALSO refers to a size (< 1mm = <10-6 m)
Sheet silicates, hydrous – some contain up to 20% H2O  together with a layered structure and weak bonding between layers make them SLIPPERY WHEN WET
Very complex (even argued) chemistry reflective of specific solution compositions

7. Major Clay Minerals Kaolinite – Al2Si2O5(OH)4
Illite – K1-1.5Al4(Si,Al)8O20(OH)4
Smectites:
Montmorillonite – (Ca, Na) (Al,Mg,Fe)2(Si,Al)4O10(OH)2*nH2O
Vermicullite - (Ca, Mg) (Al,Mg,Fe)3(Si,Al)4O10(OH)2*nH2O
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)

8. Phyllosilicates SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5]
Apical O’s are unpolymerized and are bonded to other constituents

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

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

11. Phyllosilicates a2 a1 Gibbsite: Al(OH)3
Layers of octahedral Al in coordination with (OH)
Al3+ 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

13. Phyllosilicates T O - T O - T O Kaolinite: Al2 [Si2O5] (OH)4
Yellow = (OH)
vdw
Kaolinite: Al2 [Si2O5] (OH)4
T-layers and diocathedral (Al3+) layers
(OH) at center of T-rings and fill base of VI layer 
vdw
weak van der Waals bonds between T-O groups

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

15. Phyllosilicates T O - T O - T O Serpentine: Mg3 [Si2O5] (OH)4
Yellow = (OH)
vdw
Serpentine: Mg3 [Si2O5] (OH)4
T-layers and triocathedral (Mg2+) layers
(OH) at center of T-rings and fill base of VI layer 
vdw
weak van der Waals bonds between T-O groups

16. 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…

17. Phyllosilicates T O T - T O T - T O T Pyrophyllite: Al2 [Si4O10] (OH)2
vdw
Yellow = (OH)
Pyrophyllite: Al2 [Si4O10] (OH)2
T-layer - diocathedral (Al3+) layer - T-layer
vdw
weak van der Waals bonds between T - O - T groups

18. Phyllosilicates T O T - T O T - T O T Talc: Mg3 [Si4O10] (OH)2
vdw
Yellow = (OH)
Talc: Mg3 [Si4O10] (OH)2
T-layer - triocathedral (Mg2+) layer - T-layer
vdw
weak van der Waals bonds between T - O - T groups

19. Phyllosilicates T O T K T O T K T O T
Muscovite: K Al2 [Si3AlO10] (OH)2 (coupled K - AlIV)
T-layer - diocathedral (Al3+) layer - T-layer - K
K between T - O - T groups is stronger than vdw

20. Phyllosilicates T O T K T O T K T O T
Phlogopite: K Mg3 [Si3AlO10] (OH)2
T-layer - triocathedral (Mg2+) layer - T-layer - K
K between T - O - T groups is stronger than vdw

21. Phyllosilicate Structures
A Summary of
Phyllosilicate Structures
Fig Klein and Hurlbut Manual of Mineralogy, © John Wiley & Sons

22. Carbonate Minerals Calcite Group (hexagonal)
Dolomite Group (hexagonal)    
AragoniteGroup (orthorhombic)        
mineral
formula
Calcite
CaCO3
Dolomite
CaMg(CO3)2
Aragonite
Magnesite
MgCO3
Ankerite
Ca(Mg,Fe)(CO3)2
Witherite
BaCO3
Siderite,
FeCO3
Kutnohorite
CaMn(CO3)2
Strontianite
SrCO3
Rhodochrosite
MnCO3

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

24. Dolomite Group
Similar structure to calcite, but Ca ions are in alternating layers from Mg, Fe, Mn, Zn
Ca(Mg, Fe, Mn, Zn)(CO3)2
Ca  Dolomite
Fe  Ankerite
Mn  Kutnahorite

25. 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….)

26. 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