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Mineral Aggregates
J. D. Price
Natural Science II – ERTH 1040
More than one crystal…
more than one bubble
Image from Smith, 1964
This will happen to
any polycrystalline
material given
enough energy
(e.g. heat) and
time.
More names (pause for groaning)…
Mineral names, although numerous, correspond to
a composition and structure.
Rock names are less specific
Subdivided into Igneous, Metamorphic, and
Sedimentary.
Igneous further subdivided by crystal size and
classified by composition
Metamorphic classified by texture and
composition
Sedimentary classified by composition, origin,
and texture (in that order)
Igneous (form from melts)
Mafic (plagioclase,
pyroxene, olivine)
Basalt
Gabbro
Anorthosite
Ultramafic
(pyroxene, olivine)
Peridotite
Felsic (feldspar,
quartz)
Rhyolite
GraniteIntermediate (feldspar,
pyroxene, amphibole)
Andesite
Tonalite
Sedimentary (form near surface)Clastic
Mostly silicate minerals
Conglomerate (rocks)
Sandstone (quartz, alkali
feldspar)
Shale (clay minerals)
Mudstone (clay minerals)
Biogenic
Carbonate minerals
Limestone (calcite)
Dolostone (dolomite)
Chemogenic
Halide, sulfate, carbonate
Evaporites (gypsum,
anhydrite, halides)
Speleothems, tufa (calcite)
Metamorphic (heated and pressurized)
Slate (silicate) Schist (silicate) Gneiss (silicate)
Quartzite (silicate - quartz) Ecologite (mafic silicate)
Marble (carbonate) Granulite (silicate)
Low Grade High Grade
R O C K S
1. Precipitants and water-lain
fragments, low T and P,
Sedimentary.
2. Re-equilibrated materials, wide
range of T and P, Metamorphic.
3. Melted materials, high T, Igneous.
Me
ch
an
ica
l
Ch
em
ica
l
Assembling minerals
Energies
Igneous rocks are the end products of partial
melting in the earth, so their compositions are
determined by the chemical processes
involved in melting earth materials
Source, conditions, and degree of melting
Q: What is the dominant rock
type on Earth?
Partially molten rock is called magma
(crystals, liquid, and vapor).
Magmas arise from partial melting of a source rock.
They may or may not separate entirely from the
source.
Recall that magmas are typically more buoyant than
surrounding rocks – move upwards
Magmas that move to the surface (at volcanoes)
are termed volcanic.
Typically results in crystals less than 1 mm long
Magmas that stop at depth are termed plutonic
Typically results in crystals more than 1 mm long
Ultramafic (very Mg-Fe rich) rocks
Coarse: Dunite, Lherzolite, Harzburgite, Periodotite
Fine: Kimberlite
Minerals: these are rocks largely comprised of olivine
(isolated silicate) and pyroxene (single-chain silicate)
Origin: solidification of early Earth
Location: the mantle
Univ. North Carolina, Atlas of rocks,
minerals, and textures website
Mafic (Mg-Fe rich) Rocks
Coarse: Gabbro, Anorthosite Fine: Basalt
Minerals: Largely olivine (isolated), pyroxene (single-
chain), and feldspar (framework).
Origin: Partial melting of the mantle
Oceanic crust, oceanic islands, the moon.
Univ. North Carolina, Atlas of rocks, minerals,
and textures website
Anorthosite
Univ. North Dakota, Plutonic Images
Basalt
Gabbro
Univ. North Carolina, Atlas of rocks, minerals,
and textures website
Intermediate rocks (less Fe-Mg, more Na-K-Si-Al)
Coarse: Granodiorite, Tonalite Fine: Andesite, Dacite
Minerals: Feldspar (framework), pyroxene (single
chain), amphibole (double chain), and quartz
(framework)
Origin: liquid fraction of crystallizing mafic liquids.
Location: Convergent tectonic settings
Tonalite
Felsic (K, Na, and Si rich) rocks
Coarse: Granite
Fine: Rhyolite
Minerals: Feldspar and quartz (framework), with small
amounts of amphibole (double chain) and mica (sheet).
Origins: Partial melting of crustal rocks and liquid
fraction of crystallizing intermediate liquids.
Location: continental magmatism
Granite
Univ. North Carolina, Atlas of rocks,
minerals, and textures website
Rhyolite
Vitrophyre
©Pam Gore, GPC
Felsic rocks
Q: What is the structure of glass?
Olivine
Pyroxene
Hornblende
Biotite
Muscovite
Quartz
Ca - Feldspar
Na - Feldspar
Hig
h T
em
pL
ow
Tem
p
K - Feldspar
Mafic
Intermediate
Felsic
Less s
tab
le
At
Su
rface
Mo
re s
tab
le
At
su
rface
Less A
l, S
i, K
Mo
re A
l, S
i, K
Mo
re F
e, M
g, C
aL
ess F
e, M
g, C
a
Ultramafic
Rocks from melts – overview
Weathering
Question: What rocks are high temperature? Why?
Press and Sevier, 1986
Weathering & Erosion
Q: What is the difference between
weathering and erosion?
Particles settling under
the influence of gravity.
•Clastic: pieces of
older rocks
•Biogenic: fragments
of dead organisms
•Chemogenic:
particles precipitated
from solution
Sedimentation
Deposition
Coral reef
River channel
Delta
Dune
Layeringresults from horizontal
deposition
Q: Why are the layers inclined on the right photo?
Compaction, Limited re-equilibration, and
Cementation
•Continuing deposition, sediments buried (increase
in P < 500 MPa or 5 kbar and T < 100 oC).
•Sediments are frequently porous (grainsize
dependent), lots of fluids.
•Low-T minerals grow, typically between grains
Diagenesis
Q: What are the two biggest
processes in lithifacation?
Compaction and cementation
Figure 19.12a
As sediments accumulate,
the additional weight of new
particles pushes down on
those below, compacting the
material.
Because sediments largely
accumulate in water-filled
basins, groundwater moves
through the sediments, and
may precipitate minerals in
the pores which bind the
rock.
Preservation
Modern desiccation
cracks in mud
300 Ma desiccation
cracks in shale
Fragments of pre-existing rocks, produced by
weathering and erosion.
Weathering - mechanical and chemical breakdown
of rocks and minerals.
Erosion - fragments are moved away from source
(downhill).
May operate together or separately.
Clastics are categorized first by grain size and then by
composition.
Clastic
Chemical and mechanical breakdown of rocks results
in particles of increasingly smaller size.
Earth scientists have formal names for size ranges
Cobble > 10 mm
Gravel 1 mm – 10 mm
Clastic particles
transported by water
movement
Conglomerate
Large particles of eroded rock, typically embedded in
finer particles (typically silicate)
Origin: High energy fluid transport
James Madison Univ. Sedimentology
Sandstone
Sand sized particles (typically quartz, feldspar, or rock
fragments – typically silicate) from eroded rock
Origin: Moderate energy fluid transport
Q: Is the grain-size always
uniform as shown here?
Siltstone
Silt sized particles (typically quartz and feldspar
framework silicate) from eroded rock
Origin: Low energy fluid transport
James Madison Univ. Sedimentology
Shale
Silt sized particles (typically clay – sheet silicate) from
eroded and highly weathered rock
Origin: Low energy fluid transport
James Madison Univ. Sedimentology
Q: What is the difference between
siltstone and shale?
Critters make minerals
Aragonite and calicte (both carbonates)
In general the oceans are nearly saturated in CaCO3
Ca2+ + HCO3- = CaCO3 + H+
Temperature is important (latitude)
Biogenic rocks are categorized first by composition
and then by grain size.
Biogenic Sediments
0.3mm©Ryan Hanson
Limestone
Fragmented or whole aquatic invertebrate hard parts
Origin: Bodies of water with suitable environments
Limestone
Santa Helena Cañon,
Big Bend N.P.
Chemogenic Sediments
Great Salt Lake, UT
Minerals precipitate due to
oversaturation in an evaporating
fluid.
Some form in closed bodies of
water, with significant evaporation.
Halides, sulfates, and carbonates
http://www.americansouthwest.net/
Turner Falls, OK
Q: Where have we discussed
caves (karst) previously?
Could happen to any rock
•Occurs in the solid state
•Fluids may be present
•A continuous process
Metamorphism
Two factors in metamorphic rock classification:
composition of the material and P & T conditions
However, metamorphic rocks are named using their
outward appearance
Only found in places where deformation has brought
deeper rocks to the surface.
P k
bar
Spear, 1993
All of these
conditions are
relevant to
metamorphism
on Earth. Note
that some rocks
will melt at
lower T than
others
Univ. of North Carolina Web atlas of
metamorphic textures
Slate
Conditions: relatively low P & T
Minerals: very fine grained feldspar (framework) and
mica (sheet silicates)
Origin: fine grained clastic (shale)
Q: If this rock were taken to higher T
and P, what would it look like?
Schist
Conditions: moderate P & T
Minerals: fine grained micas (sheet), some feldspar or
quartz (framework) may include garnet, staurolite
(isolated)
Origin: fine grained clastic (shale)
Univ. of North Carolina Web atlas of metamorphic textures
Marble
Conditions: low to moderate P & T
Minerals: calcite or dolomite (carbonates)
Origin: biogenic (limestone or dolostone)
Q: How is the picture on the right
similar to that on slide #3?
Univ. of North Carolina Web atlas of
metamorphic textures
Gneiss
Conditions: high P & T
Minerals: feldspar and quartz (framework), mica (sheet)
Origin: clastic (shale and sandstone), felsic (rhyolite,
granite)
Q: Is this rock similar to a coarse-
grained felsic rock (slide 14)?
Granite
Gneiss
Univ. of North Carolina Web atlas of
metamorphic textures
Eclogite
Conditions: high to very high P & T
Minerals: pyroxene, olivine, garnet
Origin: mafic (basalt, gabbro)
Q: Where might we find rocks like
these (hint: subduction)?
Granulite
Conditions: very high T & high P
Minerals: pyroxene, olivine, garnet
Origin: mafic (basalt, gabbro)
Flurry of questions (review)
•What’s type of rock is slate?
•What mineral type is found in marble?
•What elements dominate felsic rocks (note:
if you know the common elements of the
crust this will be easy)?
•What is the grainsize of a sandstone?
•What is diagenesis?
Q: What types of rock (igneous, metamorphic,
sedimentary) are found in these diagrams?
Igneousultramafic
Igneousmafic
MetamorphicHigh P, T
Sedimentarybiogenic
SedimentaryFine clastic
Igneousintermediate
All rocks are composites of minerals which
reflect the energy present at the rock’s
origin
Igneous –high heat energy, low mechanical
energy comprised of lowest energy phases for
available components in a melt
Metamorphic – moderate to high heat energy,
moderate to high mechanical energy, comprised
of lowest energy phases for available components
in a previous rock (solid)
Sedimentary – low heat energy, high mechanical
energy, comprised of a mixture of what’s available
under given mechanical energy conditions.