Sedimentary minerals ,major clay minerals

1. Major Clay Minerals
• Kaolinite – Al2Si2O5(OH)4
• Illite – K1-1.5Al4(Si,Al)8O20(OH)4
• Smectites:
– Montmorillonite – (Ca, Na)0.2-
0.4(Al,Mg,Fe)2(Si,Al)4O10(OH)2*nH2O
– Vermicullite - (Ca, Mg)0.3-
0.4(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)

2. SiO4 tetrahedra polymerized into 2-D sheets: [Si2O5]
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)
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
a1
a2

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

8. Phyllosilicates
Serpentine: Mg3 [Si2O5] (OH)4
T-layers and triocathedral (Mg2+) layers
(OH) at center of T-rings and fill base of VI layer 
Yellow = (OH)
T
O
-
T
O
-
T
O
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)(CO3)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
(hexagonal)
Dolomite Group
(hexagonal)
AragoniteGroup
(orthorhombic)
mineral formula mineral formula mineral formula
Calcite CaCO3 Dolomite CaMg(CO3)2 Aragonite CaCO3
Magnesite MgCO3 Ankerite
Ca(Mg,Fe)(
CO3)2
Witherite BaCO3
Siderite, FeCO3 Kutnohorite CaMn(CO3)2 Strontianite SrCO3
Rhodochros
ite
MnCO3

16. Carbonate Minerals
Mg Fe
Ca
Calcite, CaCO3
Dolomite
CaMg(CO3)2
Ankerite
CaFe(CO3)2
Siderite, FeCO3
Magnesite, MgCO3

17. Sulfate Minerals
• More than 100 different minerals,
separated into hydrous (with H2O) or
anhydrous (without H2O) groups
• Gypsum (CaSO4*2H2O) and anhydrite
(CaSO4) are the most common of the
sulfate minerals
• Gypsum typically forms in evaporitic basins
– a polymorph of anhydrite (g-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 (CaF2) 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
• CaF2  Ca2+ (gray)
arranged in CCP, F-
ions (red) inside
‘cage’

23. Sulfate Minerals II
• Barite (BaSO4), Celestite (SrSO4), and Anglesite
(PbSO4) 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 SO4
2- Lots of SO4
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 (Fe2O3)  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(Mn4+,Mn3+)5O10*1.34H2O  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 Mn2+Mn2
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
• 1st thing precipitated  amorphous or
extremely fine grained (nanocrystaliine) iron
oxides called ferrihydrite
Fe2+ O2

33. Ferrihydrite
• Ferrihydrite (Fe5O7OH*H2O; Fe10O15*9H2O
 some argument about exact formula) – a
mixed valence iron oxide with OH and water

34. Goethite
• Ferrihydrite recrystallizes into Goethite (a-
FeOOH)
• There are other polymorphs of iron
oxyhydroxides:
– Lepidocrocite g-FeOOH
– Akaganeite b-FeOOH

35. Iron Oxides
• Hematite (Fe2O3) – can form directly or via
ferrihydrite  goethite  hematite
• Red-brown mineral is very common in soils and
weathering iron-bearing rocks

36. • Magnetite (Fe3O4) – Magnetic mineral of
mixed valence  must contain both Fe2+
and Fe3+  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…