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Chapter 3

Minerals and Rocks

Dr. Joao Santos

Chapter 3

Minerals and Rocks

Dr. Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

• Fundamental building blocks of Earth.

• Various uses for modern economic developments.

• Important clues for figuring out the history of Earth.

• Knowledge of minerals and rocks as the first important step to better manage Earth’s resources.

Importance of Rocks and Minerals

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

• All matter, including minerals and rocks, made of atoms.

• Atom structure: Nucleus (proton and neutron) and surrounding electrons.

• Atomic number: The unique number of protons in an element’s nucleus.

• Atomic mass number: The sum of the member of protons and neutrons.

Basic Chemistry Review

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Rock-Forming Mineral Groups

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Minerals

� Minerals are the “building blocks” of rocks—hence, Earth.

� More than 4,000 are known.

� Dozens of new minerals are discovered annually.

� Human interest in minerals spans millennia.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Minerals � Developed societies depend on mineral resources.

� Metals – Iron, copper, lead, zinc, nickel, aluminum, etc.

� Non-metals – Gypsum, limestone, aggregate, clay.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Minerals

Figure 3.2b

Figure 3.1

Figure 3.2a

� Economically important – Drive world economies.

� Historically important – Dictated human history.

� Iron.

� Copper.

� Gold.

� Diamonds.

� Gems.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Rocks � Rocks are earth materials made from minerals.

� Most rocks contain more than one kind of mineral.

� Example: Granite

�K-feldspar – Pink.

�Quartz – Gray.

�Hornblende – Black.

� Some are monomineralic.

� Limestone (Calcite)

� Rock salt (Halite)

� Glacial ice.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Mineral Physical Properties

PyritePyrite

� Characteristics determined by your five senses.

� Used to ID minerals.

� Properties depend upon…

� Chemical composition.

� Crystal structure.

� Some are diagnostic.

Example: Pyrite (FeS2)

Cubic crystals, high specific gravity, striated crystal faces, black streak, metallic luster, dull brassy color, sulfur smell when crushed, erroneously mistaken for gold (fool’s gold).

� Minerals have unique sets of physical properties.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Mineral Physical Properties

Needle-like crystal habit

� Common properties of

minerals are...

� Crystal form.

� Crystal habit.

� Luster.

� Color.

� Streak.

� Hardness.

� Cleavage.

� Fracture.

� Specific gravity.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Color

Quartz – Many colorsQuartz – Many colors Malachite – Always greenMalachite – Always green

� Color is diagnostic for some minerals.

� Olivine is olive green.

� Azurite is always blue.

� Some minerals may exhibit a broad color range.

� Quartz (Clear, white, yellow, pink, purple, gray, etc).

� Color varieties often reflect trace impurities.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Streak

Hematite – Red-brown streakHematite – Red-brown streak

� Mineral color crushed on an unglazed porcelain plate.

� Streak is often a useful diagnostic property.

� Congruent streak – Streak color the same as the mineral.

�Magnetite – Black mineral; black streak.

� Incongruent streak – Streak color differs from the mineral.

�Chromite – Black mineral; greenish-brown streak.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Luster

Satin spar Gypsum – Satiny lusterSatin spar Gypsum – Satiny luster

Quartz – Vitreous lusterQuartz – Vitreous luster

� The way a mineral surface scatters light.

� Two subdivisions.

� Metallic – Looks like a metal.

� Nonmetallic.

�Vitreous (glassy).

�Satiny.

�Silky.

�Resinous.

�Pearly.

�Earthy (dull).

�Adamantine (brilliant).

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

� Scratching resistance of a mineral.

� Hardness compared to the Mohs hardness scale.

� Talc, Graphite.

� Gypsum.

� Calcite.

� Fluorite.

� Apatite.

� Orthoclase.

� Quartz.

� Topaz.

� Corundum.

� Diamond.

Hardness

Glass - Steel 5.5

Fingernail 2.5

Copper Penny 3.5

Steel File 6.5

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

PyritePyrite

Specific Gravity

Potassium FeldsparPotassium Feldspar

� Related to density (mass per volume)

� Mineral weight over weight of equal water volume.

� Specific gravity is “heft”– How heavy it feels.

� Pyrite – Heavy (SG 5.0)

� Feldspar – Light (SG 2.6)

� Pyrite “feels” heavier than feldspar.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Crystal Habit

Cubes Hexagonal PrismsBlades

RhombohedraDodecahedra

Octahedra

Tetragonal PrismsCompound Forms

� Crystal habit is the ideal shape of crystal faces.

� Ideal faces require ideal growth conditions.

� Many descriptive terms are used to characterize habit.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Crystal Form

Amethyst GeodeAmethyst Geode

� Minerals vary in crystal face development.

� Euhedral – Good crystal faces; grown in open cavity.

� Anhedral – No crystal faces; grown in tight space.

� Subhedral – Between the two.

� Face development indicates growth history.

� Anhedral crystals common; euhedral less so.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Cleavage � Tendency to break along planes of lattice weakness.

� Cleavage produces flat, shiny surfaces.

� Described by the number of planes and their angles.

� Sometimes mistaken for crystal habit.

� Cleavage is through going; often forms parallel “steps”.

� Habit is only on external faces.

� 1, 2, 3, 4, and 6 cleavages possible.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Cleavage

Muscovite MicaMuscovite Mica

AmphiboleAmphibole

Potassium FeldsparPotassium Feldspar

� Examples of Cleavage:

� 1 direction

� 2 directions at ~ 90º

� 2 directions NOT at 90º

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Cleavage

CalciteCalcite

HaliteHalite � Examples of Cleavage:

� Three directions at 90º

� Three directions NOT at 90º

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Fracture

ObsidianObsidian

� Some minerals lack planes of lattice weakness.

� Due to equal molecular bonds in all directions.

� These minerals don’t cleave; they exhibit fracture.

� Example: Quartz displays conchoidal fracture.

�Shaped like the inside of a clam shell.

�Breaks along smooth, curved surfaces.

�Produces extremely sharp edges.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Mineral Compositions

74.3% of crustal minerals !!!

� Only about 50 minerals are abundant.

� 98% of crustal mineral mass is from eight elements.

� Oxygen O 46.6%

� Silicon Si 27.7%

� Aluminum Al 8.1%

� Iron Fe 5.0%

� Calcium Ca 3.6%

� Sodium Na 2.8%

� Potassium K 2.6%

� Magnesium Mg 2.1%

� All others 1.5%

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

Mineral Classes

Fluorite (Halide) Native CopperMalachite (Carbonate)

� Minerals are classified based upon the dominant anion.

� Silicates SiO2 4- Rock-forming minerals

� Oxides O2- Magnetite, Hematite

� Sulfides S- Pyrite, Galena

� Sulfates SO4 2- Gypsum

� Halides Cl- or F- Fluorite, Halite

� Carbonates CO3 2- Calcite, Dolomite

� Native elements Cu, Au, C Copper, Gold, Graphite

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 3: Patterns in Nature: MineralsChapter 3: Patterns in Nature: Minerals

• Aggregated solids of minerals.

• Three major types of rocks classified by origin, the way the rocks formed.

• Fundamental links between rocks and environment (resources, sources for acid rain drainage, land subsidence, structure foundation failures, etc.).

• Rocks deform in response to geologic forces/stress.

Rocks

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Igneous Rocks � Solidified molten rock.

� 1,100°°°°C to 650°°°°C.

� Temp depends on composition.

� Earth is mostly igneous rock.

� Magma – Subsurface melt.

� Lava – Melt at the surface.

� Volcanoes erupt magma.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Igneous Rocks � Melted rock can cool above or below ground.

� Intrusive igneous rocks – Cool slowly underground.

� Extrusive igneous rocks – Cool quickly at the surface.

�Lava – Cooled liquid.

�Pyroclastic debris – Cooled fragments.

�Volcanic ash.

�Fragmented lava.

� Many types of igneous rocks.

� All oceanic crust.

� Most continental crust.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

What is Magma Made of? � Magmas have three components (solid, liquid and gas).

� Solid – Solidified mineral crystals are borne by the melt.

� Liquid – The melt itself is comprised of mobile ions.

�Dominantly Si and O; lesser Al, Fe, Mg, and K.

�Other ions present to a lesser extent.

� Different mixes of elements yield different magmas.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

What is Magma Made of? � Gas – Magmas contain abundant dissolved volatile gas.

�Dry magma – Scarce volatiles.

�Wet magma – To 15% volatiles.

�Water vapor (H2O)

�Carbon dioxide (CO2)

�Sulfur dioxide (SO2)

�Nitrogen (N2)

�Hydrogen (H2)

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Magma Compositions � There are four major magma types based on silica (SiO2)

percentage.

� Felsic (feldspar and silica) 66 to 76% SiO2.

� Intermediate 52 to 66% SiO2.

� Mafic (Mg and Fe-rich) 45 to 52% SiO2.

� Ultramafic 38 to 45% SiO2.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Magma Compositions � Composition controls magma density, T, and viscosity.

� The most important factor is silica (SiO2) content.

�Silica-rich magmas are thick and viscous.

�Silica-poor magmas are thin and “runny.”

� These characteristics govern eruptive style.

Type Density Temperature Viscosity

Felsic Very low Very low (600 to 850°°°°C) Very High: Explosive eruptions.

Intermediate Low Low High: Explosive eruptions.

Mafic High High Low: thin, hot runny eruptions.

Ultramafic Very high Very high (up to 1300°°°°C) Very low.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Igneous Environments � Two major categories – Based on cooling site.

� Extrusive settings – Cool at or near the surface.

�Cool rapidly.

�Chill too fast to grow big crystals.

� Intrusive settings – Cool at depth.

�Lose heat slowly.

�Crystals grow large.

� Most mafic magmas extrude.

� Most felsic magmas don’t.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Interlocking or crystalline texture

Igneous Textures � The size, shape, and arrangement of the minerals.

� Interlocking – Mineral crystals fit like jigsaw puzzle pieces.

� Fragmental – Pieces of preexisting rocks, often shattered.

� Glassy – Made of solid glass or glass shards.

Glassy texture

Fragmental texture

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Crystalline Igneous Textures � Texture reveals cooling history.

� Aphanitic (finely crystalline).

�Rapid cooling.

�Crystals do not have time to grow.

�Extrusive.

� Phaneritic – (coarsely crystalline).

�Slow cooling.

�Crystals have a long time to grow.

�Intrusive.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Igneous Classification � Classification is based upon composition and texture.

� Composition – Felsic, intermediate, mafic, and ultramafic.

� Texture – Fine (aphanitic); coarse (phaneritic).

Type Aphanitic (fine) Phaneritic (coarse)

Felsic Rhyolite Granite

Intermediate Andesite Diorite

Mafic Basalt Gabbro

Ultramafic Very high Very high (up to 1300°°°°C)

A B

C2 C1

C2C1

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

� Form by very rapid cooling of lava in water or air.

� Glassy textures are more common in felsic magmas.

� They often preserve gas bubbles (vesicles).

� Underwater, basalt lava quenches into “pillows.”

Glassy Textures

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Glassy Classification � Glassy Igneous Rocks.

� Obsidian – Volcanic glass from rapidly cooled lava.

�Quenching – Lava flowing into water.

�High silica lavas – These can make glass without quenching.

� Pumice – Frothy felsic rock full of vesicles; it floats.

� Scoria – Glassy, vesicular, mafic rock.

Pumice Scoria Obsidian

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Fragmental Textures � Preexisting rocks that were shattered by eruption.

� After fragmentation, the pieces fall and are cemented.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 4: Up from the Inferno: Igneous RocksChapter 4: Up from the Inferno: Igneous Rocks

Fragmental Classification � aka Pyroclastic – Fragments of violent eruptions.

� Tuff – Volcanic ash that has fallen on land and solidified.

� Volcanic breccia – Made of larger volcanic fragments.

Tuff Breccia

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 6: Pages of Earth’s Past: Sedimentary RocksChapter 6: Pages of Earth’s Past: Sedimentary Rocks

Sedimentary Rocks � Sediments are the building blocks of sedimentary rocks.

� Sediments are diverse, as are the rocks made from them.

� Four classes:

� Clastic – Made from weathered rock fragments (clasts).

� Biochemical – Cemented shells of organisms.

� Organic – The carbon-rich remains of plants.

� Chemical – Minerals that crystallize directly from water.

ChemicalClastic OrganicBiochemical

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Clastic Sedimentary Rocks � Clastic sedimentary rocks reflect several processes.

� Weathering – Generation of detritus via rock disintegration.

� Erosion – Removal of sediment grains from rock.

� Transportation – Dispersal by wind, water, and ice.

� Deposition – Settling out of the transporting fluid.

� Lithification – Transformation into solid rock.

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� Lithification – Transforms loose sediment into solid rock.

� Burial – More sediment is added onto previous layers.

� Compaction – Overburden weight reduces pore space.

�Sand – 10 to 20%

�Clay – 50 to 80%

� Cementation – Minerals grow in pores, “gluing” sediments.

Clastic Sedimentary Rocks

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Clastic Sedimentary Rocks � Clast (grain) size – The average diameter of clasts.

� Range from very coarse to very fine.

� Boulder, cobble, pebble, sand, silt, and clay.

� With increasing transport, average grain size decreases.

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Clastic Sedimentary Rocks � Clast composition – The mineral makeup of sediments.

� May be individual minerals or rock fragments.

� Mineral identities provide clues about…

�The source of the sediment.

�The environment of deposition.

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Clastic Sedimentary Rocks � Angularity and sphericity – Indicate degree of transport.

� Fresh detritus is usually angular and non-spherical.

� Grain roundness and sphericity increases with transport.

� Well-rounded – Long transport distances.

� Angular – Negligible transport.

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Clastic Sedimentary Rocks � Sorting – The uniformity of grain size.

� Well-sorted – Uniform grain sizes.

� Poorly sorted – Wide variety of grain sizes.

� Sorting becomes better with distance from source.

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Clastic Sedimentary Rocks � Coarse clastics – Composed of gravel-sized clasts.

� Breccia – Comprised of angular fragments.

�Angularity indicates a lack of transport processing.

�Deposited relatively close to source.

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Clastic Sedimentary Rocks � Coarse clastics – Composed of gravel-sized clasts.

� Conglomerate – Comprised of rounded gravel.

�Indicates water transport.

�Clasts bang together forcefully in flowing water.

�Collisons round angular corners and edges of clasts.

�Conglomerates are deposited at a distance from the source.

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Clastic Sedimentary Rocks � Sandstone – Clastic rock made of sand-sized particles.

� Forms in many depositional settings.

� Quartz is, by far, the dominant mineral in sandstones.

� Sandstone varieties.

� Arkose – Contains abundant feldspar.

� Quartz sandstone – Almost pure quartz.

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Clastic Sedimentary Rocks � Fine clastics - Composed of silt and clay.

� Silt-sized sediments are lithified to form siltstone.

� Clay-sized particles form shale.

� Fine clastics are deposited in quieter waters.

� Floodplains, lagoons, mudflats, deltas, deep-water basins.

� Organic-rich shales are the source of petroleum.

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� These are sediments derived from living organisms.

� Biochemical – Hard mineral skeletons.

� Organic – Cells of plants, algae, bacteria and plankton.

Biochemical and Organic Rocks

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Biochemical Rocks � Biochemical limestone – CaCO3 skeletal (shell) remains.

� Warm, tropical, shallow, clear, O2-rich, marine water.

� Diverse organisms (plankton, corals, clams, snails, etc.).

� Many textural varieties.

�Reefs.

�Shell debris.

�Lime mud (micrite).

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� Chert – Rock made of cryptocrystalline quartz.

� Formed from opalline silica (SiO2) skeletons.

�Diatoms.

�Radiolarians.

� Opalline silica added to bottom sediments dissolves.

� Silica pore fluids solidify to form chert nodules or beds.

Biochemical Rocks

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� Made from organic carbon.

� Coal – Altered remains of fossil vegetation.

�Accumulates in lush tropical wetland settings.

�Requires deposition in the absence of oxygen.

� Oil shale – Shale with heat altered organic matter.

Organic Rocks

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Chemical Sedimentary Rocks � Comprised of minerals precipitated from water solution.

� Evaporites – Created from evaporated seawater.

� Evaporation triggers deposition of chemical precipitates.

� Examples include halite (rock salt) and gypsum.

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Chemical Sedimentary Rocks � Travertine – Calcium carbonate (CaCO3) precipitated

from groundwater where it reaches the surface.

� Dissolved calcium (Ca2+) reacts with bicarbonate (HCO3 -).

� CO2 expelled into the air causes CaCO3 to precipitate.

�Thermal (hot) springs.

�Caves.

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Chemical Sedimentary Rocks � Dolostone – Limestone altered by Mg-rich fluids.

� CaCO3 altered to dolomite CaMg(CO3)2 by Mg 2+-rich water.

� Dolostone looks like limestone, except…

�It has a sugary texture and a pervasive porosity.

�It weathers to a buff, tan color.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Metamorphic – Changed from an original “parent.”

� Meta = Change.

� Morph = Form or shape.

� Parent rocks are called

“protoliths.”

� Metamorphism can

occur to any protolith.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Protoliths undergo pronounced changes in…

� Texture.

� Mineralogy.

� Due to changes in…

� Temperature.

� Pressure.

� Tectonic stress.

� Reaction with heated water.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Character � Metamorphic rocks have distinctive properties.

� Unique texture – Intergrown and interlocking grains.

� Unique minerals – Some that are only metamorphic.

� Unique foliation – A planar fabric from aligned minerals.

� These transformations can change the rock completely.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Processes � Metamorphic change occurs slowly in the solid state.

� Several processes are at work.

� Recrystallization – Minerals change size and shape.

� Phase change – New minerals form with…

�Same chemical formula.

�Different crystal structure.

�Example: Kyanite.

KyaniteKyanite

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Processes � Neocrystallization – New minerals with changes in

temperature and pressure.

� Initial minerals become unstable and change to new minerals.

�Original protolith minerals are digested in reactions.

�Elements restructure to form new minerals.

� In this way, a shale can transform into a garnet mica schist.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Processes � Pressure solution – Mineral grains partially dissolve.

� Dissolution requires small amounts of water.

� Minerals dissolve where their surfaces press together.

� Ions from the dissolution migrate in the water film.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Processes � Plastic deformation – Mineral grains soften and deform.

� Requires elevated temperatures.

� Rock is squeezed or sheared.

� Minerals act like plastic, changing shape without breaking.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Causes of Metamorphism � The agents of metamorphism are…

� Heat (T).

� Pressure (P).

� Compression and/or shear.

� Hot water.

� Not all agents are required; they often do co-occur.

� Rocks may be overprinted by multiple events.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Heat (Temperature, T) � Metamorphism occurs as the result of heat.

� Temperature (T) ranges between 200oC and 850oC.

� The upper T limit is…melting. It varies based upon rock mineral composition and water content.

� Heat energy breaks and reforms atomic bonds.

� Sources of heat.

� Magmatic intrusions.

� Compression.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Pressure (P) � P increases with depth in the crust.

� 270 to 300 bars per km (1 bar is almost 1 atm = 14.7 psi).

� Metamorphism occurs mostly in 2 to 12 kbar range.

� T and P both change with depth.

� Mineral stability is highly dependent upon T and P.

� This stability can be graphed on a “phase diagram.”

� Changes in T and P lead

to changes in minerals.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

� Pressure that is greater in one orientation.

� A commonplace result of tectonic forces.

� Two kinds of differential stress: Normal and shear.

� Normal Stress – Operates perpendicular to a surface.

�Tension – Pull-apart normal stress.

�Compression – Push-together normal stress.

Differential Stress

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Differential Stress � Two kinds of differential stress: Normal and shear.

� Shear Stress – Operates sideways across a surface.

�Causes material to be “smeared out.”

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

� At higher T and P, differential stress deforms rock.

� Rocks change shape slowly without breaking.

Differential Stress

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Hydrothermal Fluids � Hot water with dissolved ions and volatiles.

� Hydrothermal fluids facilitate metamorphism.

� Accelerate chemical reactions.

� Alter rocks by adding or subtracting elements.

� Hydrothermal alteration is called metasomatism.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rock Types � Two major subdivisions of metamorphic rocks.

� Foliated – Has a through-going planar fabric.

�Subjected to differential stress.

�Classified by composition, grain size, and foliation type.

Edited by Joao Santos

Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rock Types � Two major subdivisions of metamorphic rocks.

� Nonfoliated – No planar fabric evident.

�Crystallized without differential stress.

�Classified by mineral composition.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Slate – Fine clay, low-grade metamorphic shale.

� Has a distinct foliation called slaty cleavage.

�Develops by parallel alignment of platy clay minerals.

�Slaty cleavage oriented perpendicular to compression.

�Slate breaks along this foliation creating flat sheets.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Phyllite - Fine mica-rich rock.

� Formed by low- to medium-grade alteration of slate.

� Clay minerals neocrystallize into tiny micas.

� Micas reflect a satiny luster.

� Phyllite is between slate and schist.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

� Schist – Fine or coarse rock with larger micas.

� Medium- to high-grade metamorphism.

� Has a distinct foliation called schistosity.

�Parallel alignment of large mica crystals.

�Micas are visible because they have grown at higher T.

� Schist often has other minerals due to neocrystallization.

�Quartz.

�Feldspars.

�Kyanite.

�Garnet.

�Staurolite.

�Sillimanite.

� Large non-mica minerals are called porphyroblasts.

Metamorphic Rocks

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Gneiss – Has a distinct banded foliation.

� Light bands of felsic minerals (quartz and feldspars).

� Dark bands of mafic minerals (biotite or amphibole).

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Compositional banding develops in several ways.

� Original layering in the protolith.

� Extensive high-temperature shearing.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Migmatite � Migmatite is a partially melted gneiss.

� It has features of igneous and metamorphic rocks.

� Mineralogy controls behavior.

� Light-colored (felsic) minerals melt at lower T.

� Dark-colored (mafic) minerals melt a higher T.

� Felsics melt first; mafics remain metamorphic.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Nonfoliated rocks lack a planar fabric.

� Absence of foliation possible for several reasons:

�Rock not subjected to differential stress.

�Dominance of equant minerals.

�Absence of platy minerals like clays or micas.

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Amphibolite – Dominated by amphibole minerals.

� Basalt or gabbro protolith.

� Usually not well foliated.

� Hornfels – Alteration by heating.

� Associated with plutonic intrusions.

� Finely crystalline.

Amphibolite Hornfels

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Quartzite – Almost pure quartz in composition.

� Forms by alteration of quartz sandstone.

� Sand grains in the protolith recrystallize and fuse.

� Like quartz, it is hard, glassy, and resistant.

Metamorphic Alteration

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Metamorphic Rocks � Marble - Coarsely crystalline calcite or dolomite.

� Forms from a limestone or dolostone protolith.

� Extensive recrystallization completely changes the rock.

� Original textures and fossils in the parent are obliterated.

� Used as a decorative and monument stone.

� Exhibits a variety of colors.

Metamorphic Alteration

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Essentials of Geology, 3rd edition, by Stephen MarshakEssentials of Geology, 3rd edition, by Stephen Marshak Chapter 7: Metamorphism: A Process of ChangeChapter 7: Metamorphism: A Process of Change

Rock Cycle

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End of Chapter 3