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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
Clays
Sheet Silicates – aka Phyllosilicates
[Si2O5]2Sheets of tetrahedra
micas talc clay minerals serpentine
Phyllosilicates
Sheet Silicates – aka Phyllosilicates
[Si2O5]2Sheets of tetrahedra
micas talc clay minerals serpentine
Phyllosilicates
•Clays  talc  pyrophyllite  micas
•Display increasing order and lower variability of
chemistry as T of formation increases
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
Major Clay Minerals
• Kaolinite – Al2Si2O5(OH)4
• Illite – K1-1.5Al4(Si,Al)8O20(OH)4
• Smectites:
– Montmorillonite – (Ca, Na)0.20.4(Al,Mg,Fe)2(Si,Al)4O10(OH)2*nH2O
– Vermicullite - (Ca, Mg)0.30.4(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)
Clay building blocks
• Kaolinite micelles attached with
H bonds – many H bonds
aggregately strong, do not
expend or swell
1:1 Clay
Clay building blocks
• 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…
2:1 Clay
Cement
• Mixture of lime (CaO – made by roasting
calcite) and silicates made by sintering
limestone and clay
• Ancient cement was just CaO – mixed with
water to form portlandite (Ca(OH)2), which
then slowly reacted with CO2 to reform
calcite
• Modern cement is mixed with water, form
several Ca-Si phases that are more durable
and don’t shrink as much
Carbonate Minerals
Ca
Calcite, CaCO3
Dolomite
CaMg(CO3)2
Magnesite, MgCO3
Mg
Ankerite
CaFe(CO3)2
Siderite, FeCO3
Fe
Calcite Group
• Variety of minerals varying
by cation
• Ca  Calcite
• Fe  Siderite
• Mn  Rhodochrosite
• Zn  Smithsonite
• Mg  Magnesite
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
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….)
Calcite vs. Dolomite
• dolomite less reactive with HCl calcite, has
lower indices of refraction
• dolomite more commonly euhedral and
twinned
• calcite commonly colorless
• dolomite may be cloudy or stained by iron
oxide
• Mg  spectroscopic techniques!
• Different symmetry  cleavage same, but
easily distinguished by XRD
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)
Gypsum
• 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)
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)
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)
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 SO42Not very much Ba, Sr, Pb
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
Opal - Gemstone
Agates