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.

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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

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Tem

p

K - Feldspar

Mafic

Intermediate

Felsic

Less s

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At

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Mo

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At

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Less A

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Mo

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Mo

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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.