Geology Test #3

The important characteristics of surface conditions that lead to chemical weathering

the presence of water (in the air and on the ground surface), the abundance of oxygen, and the presence of carbon dioxide, which produces weak carbonic acid when combined with water.

Evaporites

the product of saltwater evaporation. Can only occur when lake has no outlet so as evaporation increases, dissolved ions become more concentrated Gypsum (CaSO4) and /or Halite (NaCl)

The colder the climate...

the slower the process

Lithification

the transformation of loose sediment into solid rock

In the presence of oxygen, the dissolved iron is

then quickly converted to hematite

The amount of CO2 in the air is enough to make only very weak carbonic acid, but

there is typically much more CO2 in the soil, so water that percolates through the soil can become significantly more acidic.

quartz

virtually unaffected by chemical weathering

degree of chemical weathering is greatest in

warm and wet climates

H2O + CO

—->H2CO3

Chemical sedimentary rocks types

1) Evaporites 2) Dolostones 3) Chert (chemical chert) 4) Travertine (chemical Limestone)

karst topography Is characterized by

1) Sinkholes: surface depressions formed by the collapse of caves or other underground void spaces 2) Springs: places where water flows naturally from the ground (from spaces in the bedrock). 3) Disappearing streams: streams that terminate abruptly by seeping into the ground.

Weathering

General process by which rocks are broken down at Earth's surface

H2O + CO —->H2CO3 water + carbon dioxide —-> carbonic acid THEN...

H2CO3 —-> H+ + HCO3-, carbonic acid —-> hydrogen ion + bicarbonate ion

Oxidation

Oxidation reactions in rocks transform iron-bearing minerals into a rusty-brown mixtures of various iron-oxide and iron-hydroxide minerals, such as hematite (Fe2O3), goethite (α-FeO(OH), and limonite (FeO(OH)·nH2O

Hydrolysis

Potassium feldspar, a common mineral in granite, reacts with acidic water (carbonic acid) to produce kaolinite (a type of clay) and other dissolved ions Hydrolysis reactions break down not only feldspars, but many other silicate minerals as well, amphiboles, pyroxenes, micas, and olivines.

Monument Valley, Arizona.

Red and brown iron oxides color weathering rocks in

Tower Karst Landscape in the Guilin region of China:

Ridges or walls between adjacent sinkholes tend to be steep-sided, for they were originally joint controlled. Over time, the walls erode, leaving only jagged, isolated spires3⁄4 a karst landscape dominated by such spires is called tower karst.

Angularity of particle types

Rounded--Subrounded--Subangular--angular

Sediments include

Sand, Mud, gravel, dust, calcified organisms, saline precipitates

dissolution

Some minerals dissolve completely, and their components go into solution. For example, calcite (CaCO3) is soluble in acidic solutions

Sedimentary Transport Agents

Waves, Lake currents, River currents, Wind, Ice, Meltwater, ocean currents, Turbidity currents, Tidal currents, Tides

Greek ruins at Segesta, Italy

Weathered limestone blocks and columns of 2500-year-old

Bicarbonate ions react with feldspar

Weathering it to kaolinite clay and silicateand releasing bicarbonate and potassium ions.

Karst Topography - China

World Heritage listed. It covers half a million square kilometers (193,000 square miles) of southern and central China. China's limestone landscapes are uniquely big and unusually interesting

Sinkholes

a small, steep depression in the land surface above the cavernous limestone formation

Ferriciron Fe(III) combines with water to precipitate

a solid,iron oxide, from solution

Carbonic acid ionizes to form

hydrogen ions (H+) and bicarbonate ions (HCO3-)

Agate

is chert that grows in concentric rings inside hollows in a rock and ends up with a striped appearance, caused by variations in the content of impurities while ppt. took place

Petrified wood

is chert that's made when ash from a volcanic eruption buries a forest. The ash contains silica, which dissolves in groundwater that passes into trees. Dissolved silica precipitates as cryptocrystalline quartz within wood, gradually replacing the wood's cellulose. The chert retains the shape of the wood and even its growth rings.

Dissolution of limestone

is enhanced by the atmospheric CO2 contained in rainwater. Waters that infiltrate soils may pick up even more of the gas from the CO2 given off by plant roots, bacteria, and other soil-dwelling organisms

Chemical sedimentary rocks

made up of minerals that precipitate from water solutions

Biochemical

made up of the shells of organisms

This cover ranges from

nonexistent (bare basement rocks) to almost 20 km thick beneath continental shelves. While sediments and sedimentary rocks cover more than 80% of the Earth's surface, they constitute less than 1% of the Earth's mass

1- natural zones of weakness

(Joints, fractures....etc.

Physical (mechanical)weathering

1- Natural zones of weakness (Joints, fractures....etc. 2- Exfoliation and spheroidal weathering 3- Root wedging 4- Frost wedging 5- Salt wedging 6- Differential thermal expansion of minerals creates stress in rocks e.g. Deserts 7-Other forces: rivers, glaciers, waves, burrowing creatures (from earthworms to gophers, and HUMANS (in the past century, perhaps the most energetic agents of physical weathering on the planet.

Why weathering is important

1- all the clays of the world2- all the soils of the world3- the dissolved substances that are carried by rivers to the ocean.

Three factors come into play when classifying clastic sedimentary Rocks

1- grain size 2- grain shape 3- Composition (mineral content)

Chemical effects of chemical weathering on silicates

1- it leaches, dissolves away, cations and silica 2-it hydrates, or adds water to, the minerals 3- makes the solutions less acidic

Factors that control the weathering of rocks are

1-The properties of the parent rock 2-The climate 3-The presence or absence of soil 4-The length of exposure

karst topography is Most strongly advanced in regions with:

1-high-rainfall climate, with abundant vegetation 2-extensively jointed limestone formations 3-appreciable hydraulic gradient.

glacier physical weathering

A glacier is nothing more than a frozen river still moving. It might only move an inch or two per year, but it still moves and this ice will erode the ground and rock below it faster and more aggressively than if it was just water. Its because glaciers also pick up and move the rocks that they run over and this gravel (chunks of rocks) can carve mountains down and cut valleys miles deep.

Medium Particle rocks

Arkose (sand sized quartz plus feldspar grains) Sandstone (almost pure quartz sand)

Travertine (chemical Limestone)

Around some hot springs, places where hot- water solutions spill out of the Earth, terraces of chemical limestone accumulate. Such buildups develop because when the hot water reaches the ground surface, it cools and degasses (meaning that dissolved carbonic acid bubbles off as CO2 gas, and thus can dissolve less calcite; as a result, the calcite precipitates to form rock. also makes stalecites + stalagmites

Coarse Particle rocks

Breccia + Conglomerate

Carbonic acid (H2CO3) forms when

CO2 and H2O molecules combine in rainwater.

Breakdown of calcite by carbonic acid into two water-soluble ions

Calcite + carbonic acid = Calcium ion + bicarbonate ion CaCO3 + H2CO3 = Ca2+ + 2HCO3

positive feedback

Chemical and physical weathering help and reinforce each other The faster the chemical decay (chemical weathering), the weaker thepieces and the more susceptible to breakage into smaller pieces (physical weathering). The smaller the pieces, the greater the surface area available for chemical weathering.

Karst Topography

Dissolution of limestones—or, rarely, other soluble rocks such as evaporites —by groundwater. As this CO2-rich water moves down to the water table, through the unsaturated zone to the saturated zone, it creates openings as it dissolves carbonate minerals.

half dome is what time of weathering

Exfoliation

his reaction shows potassium feldspar

Feldspar + Carbonic acid + water --> dissolved silica + dissolved potassium + dissolved bicarbonate ion

Types of chemical chert

Flint (Black chert) tools and arrowheads Jasper (Red chert) jewelry Petrified wood Agate

Chemical weathering produced by organisms

For example, roots of plants, fungi, and lichens, secret organic acids that help dissolve minerals in rocks; these organisms extract nutrients from the minerals. Microbes, such as bacteria, eat minerals for lunch

A Surface Veneer

Formed by surface processes. Sediments and sedimentary rocks are characterized by bedding

Chert (Chemical)

Formed when cryptocrystalline quartz (crypto is Greek for "hidden", quartzGrains that are too small to be seen without the extreme magnification of an electron microscope) gradually replace calcite crystals within a body of limestone.

Finer than .0039 Particle rocks

Mudstone (blocky fracture) Claystone (blocky fracture) Shale (breaks along bedding)

Sorting

the more homogeneous, the more sorted -very well sorted has more oil and gas because more space between them

biochemical Limestone

Some organisms construct their shells out of calcium (Ca)2+ and carbonate (CO3)2- ions, which they merge to make the mineral calcite (CaCO3) or its polymorph, aragonite. When the organisms die, the solid material in their shells turns into sediment that eventually becomes biochemical sedimentary rocks. Thus, biochemical sedimentary rocks consist of shells and shell debris.

examples of evaporite sites

The Bonneville Salt Flats, near the Great Salt Lake of central Utah Great Salt Lake has no outlet

Hydration

The absorption of water into the crystal structure of minerals, causes some minerals, such as certain types of clay, to expand.

Arecibo radio telescope in Puerto Rico

The dish was built by smoothing the surface of a 300-m- wide sinkhole in a karst terrain.

river physical weathering

The energy of the river directly affects what is being moved = Rivers in flood stage have greater energy, can move larger pieces with greater force. Therefore the potential for mechanical weathering is greater= Moving sand and silt acts like sandpaper on the larger rocks in the river bed and on each other.= Rocks hitting other rocks can break, making smaller pieces which can then become part of the suspended load.

Bedding:

The formation of parallel layersby the settling of particlesto the bottom of the sea, a river, or a land surface

Frost wedging

The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices water expands by 9% when it freezes

Acid Rock Drainage (ARD)

acidic water produced by the oxidation of pyrite and other minerals

Dolostone

an abundant carbonate rock composed primarily of dolomite and formed by the diagenesis of carbonate sediments and limestones Most dolomite forms by a chemical reaction between Limestone (solid calcite (CaCO3) and magnesium-bearing groundwater

Talus

an apron-shaped pile of fragmental rock, has accumulated at the base of these cliffs near Mt. Snowdon, Wales

Stalagmite

an inverted icicle-like deposit on the floor below the stalactite

Dissolved ions - weathering

are carried to the sea in streams or transported underground in groundwater. Eventually, the ions precipitate as new minerals in the sea or as new minerals filling open spaces between grains underground.

compaction (lithification)

as grains are squeezed together by the weight of overlying sediment into a mass denser than the original

cementation (lithification)

as minerals precipitate around deposited particles and bind them together.

Carbonic acid also reacts with calcitein limestone to produce

bicarbonate and calcium ions.

The dissolution of limestone breaks down

calcite by carbonic acid into two water-soluble ions Calcium ion + bicarbonate ion

Chemical weathering results from

chemical changes to minerals that become unstable when they are exposed to surface conditions

Organic sedimentary rocks

consist of carbon-rich relicts of plants

Clastic, or detrital, sedimentary rocks

consists of cemented-together detritus (solid fragments and grains) derived from preexisting rocks. "clastic", from the Greek Klastos, meaning "broken"

Sediment

consists of loose (Unconsolidated) 1) Rock fragments and or grains of minerals broken down from once-intact rock 2) Mineral crystals that precipitate directly out of water 3) Shells (forms when organisms extract ions out of water.

Sedimentary rocks represent a uniquely important rock type, for they

contain the bulk of our energy resources (e.g. Coal, Petroleum, and natural gas) and our groundwater.

Where do sedimentary rocks exist

cover much of Earth's land surface and sea floor, they form only a thin layer atop the igneous and metamorphic rocks that make up the main volume of the crust

feldspar

easily altered

The thicker the soil the

faster the process

The more organic activity the

faster the process, because of nutrients that break down into acids

Ferrous Iron Fe(II) is oxidized by oxygen molecules to form

ferric iron

Sedimentary rock

formed at or near the surface of the Earth by :1) Cementing together of loose rocks fragments or grains of minerals, 2) Cementing together of shell fragments 3) Precipitation of minerals from water solutions

Solid materials - weathering

gets picked up and moved to a new location by wind, water, or ice, until they eventually settle out. Then they either become incorporated in soil, or become buried deeply.

A special type of oxidation takes place in areas where the rocks

have elevated levels of sulfide minerals, especially pyrite (FeS2).

what made surface of mars red

oxidation

2-Exfoliation and spheroidal weathering

peeling like an onion or layers of rock

salt wedging

rock disintegration caused by the crystallization of salts from evaporating water

Limestone is a

sedimentary rock, Composed mostly of the mineral calcite (CaCO3).

Root wedging

self explanatory, roots make their way into rocks and grow bigger

Erosion

set of processes that loosen and move soil and rock downhill or downwind.

Iron pyroxene dissolves to release

silica and ferrous iron to solution

Fine particle rocks

siltstone (fine sand)

The lower the rainfall the...

slower the erosion process

Pyrite reacts with water and oxygen to form

sulfuric acid

Stalactite

suspended from the ceiling

Physical (mechanical) weathering

takes place when solid rock becomes fragmented by physical processes that do not change its chemical composition

Chemical weathering

takes place when the minerals in a rock are chemically altered or dissolved

Dissolution of limestone is enhanced by

the atmospheric CO2 contained in rainwater (carbonic acid)

The smaller the pieces

the greater the surface area available for chemical weathering