Sedimentary mineral associations

The Rock Cycle


Sedimentary Processes
1

2) & 3)
Sediments are
transported and
deposited

4


Products of weathering
Primary
Minerals

Residual
Minerals

Dissolved
Ions

Feldspar
Clay minerals K+, Ca+2, Na+
Aluminum hydroxide
Fe-Mg minerals
Limonite

Hematite &

Mg+2

Quartz Quartz Silica
Primary
Minerals

Solids that
Ions that are carried
remain in soil
away in water

----------Detrital sediments-----------------sediments

Chemical & biochemical


Types of sediment

Detrital – mineral & rock fragments

Biochemical – shells made of
calcite (CaCO3) by organisms
that extract the ions from water

Chemical – halite (NaCl) crystals
that precipitate from water


Detrital sedimentary rocks- classified by

grain size differences
Conglomerate
Breccia

Sandstone
Shale
All these rocks have clastic textures – the rocks are composed of
particles (fragments) that are cemented together


Detrital sediments are sorted by the processes of
transportation and deposition

Well sorted

Poorly sorted


Sands and sandstones can be used to interpret the erosional
history of an area and the kinds of rocks that were eroded

Wellsorted

Poorly
sorted

“Mature” sediments have little feldspar. This means that the sediment was
derived from weathered rocks or that the feldspar decomposed during
transportation in water.

The same
diagram is
used to
interpret the
provenance
(source rocks)
of sediments


Placer deposit– accumulation of sand or gravel containing minerals that are
highly resistant to chemical attack and economically valuable - gold, platinum,
ilmenite, rutile, zircon, diamond, garnet, magnetite, corundum, monazite.
These and other chemically resistant minerals are widely used to indicate the
provenance of sediments, e.g. kyanite, sillimanite, staurolite
indicate that metamorphic rocks were eroded. Diamonds indicate kimberlite;
gold indicates hydrothermal veins, etc.


Chemical and biochemical sedimentary rocks

Travertine

Coquina

Limestones – composed of calcite

Chalk

Deep ocean sediments are mainly fine-grained biochemical
sediment called oozes, with some hydrogenous (chemical)
and terrigenous (wind or water borne) detrital sediment


Calcareous & siliceous ooze
Manganese nodules are
hydrogenous - they
precipitate from deep ocean
water when the Mn oxidizes:
Mn+2 (dissolved) + O2 + 2e- =
MnO2 (pyrolusite)


Banded Iron Formations – ancient (>2.5 billion year old) sedimentary deposits of ironbearing minerals. These indicate that Earth’s early atmosphere was too poor in oxygen to
oxidize iron at the site of weathering. Dissolved iron was transported in water:
4Fe+2 (dissolved) + 3O2 = 2Fe2O3 (hematite)


Phosphates form in shallow marine environments where dissolved PO 4-3
is carried by upwelling of deep ocean water. These areas are biologically
productive - many fossils are found, especially bone material.


Phosphate Mining of the Bone Valley Formation in Florida


Evaporite minerals

Shallow basin with high rate of evaporation – Gulf of Mexico,

Persian Gulf, ancient Mediterranean Sea, Red Sea
Sequence is: calcite, gypsum, halite with increasing evaporation


Evaporites

Seawater evaporation:
1)
2)
3)
4)
5)
6)

Gypsum

Calcite
Gypsum
Anhydrite
Halite (95% evaporation)
Sylvite
Other rare minerals

Dolomite may form afterward by
reaction of Mg+2 with calcite

Continental waters:
Borax & borates
Nitrates

Halite


Salt
dome
Sulfur is
produced by
sulfate
reducing
bacteria
which
consume the
oxygen in
gypsum or
anhydrite