Chapter 2 continued

2:1 phyllosilicates

(Chlorites)

Non-silicates

2 Tetrahedral sheets

http://pubpages.unh.edu/~harter/crystal.htm#2:1%20MINERALS

+ 1 octahedral sheet

+ 1 octahedral sheet(in the interlayer)

Form “2:1:1” minerals 1:1 mineral

1.4 nm

0.7 nm

http://pubpages.unh.edu/~harter/crystal.htm

Chlorite structure2:1 interlayer

Tet.

Oct.

Tet.

Oct.2:1 layer

interlayer

2:1 Interlayer or Chlorite Minerals (formerly called 2:1:1 or 2:2 Layer Silicates)

2:1 layer silicate with positively charged Al(OH)x (Dioctahedral) or Mg(OH)x (Trioctahedral) in the interlayer (x < 3) e.g., Al(OH)2

+1

Properties:S.A. = 70-150 m2/gc-spacing = 1.4 nmNon-expansiveCEC = 10-40 cmol/kgHigh pH-dependent charge

http://www.geoclassroom.com/mineralogy/chlorite.GIF

Crystal structure of chlorite

http://www.soils.wisc.edu/courses/SS325/chlorite.gif

http://www.gly.uga.edu/schroeder/geol6550/chlorite.gif

http://www.uwm.edu/Course/422-100/Mineral_Rocks/chlorite1.jpg

Chlorite hand specimen

http://www.casdn.neu.edu/~geology/department/courses/minerals/photogallery/index.html

Non-Layer Silicates

Allophane• Amorphous (non-detectable by X-Ray Diffraction)• Derived from volcanic ash in relatively young soils -

the rapid cooling of lava ejected from volcanoes leads to deposition of much of the ash as amorphous glasses. Amorphous gels of silica, alumina, and silica-alumina polymers are formed during decomposition of the ash.

• (Al2O3) (Fe2O3) SiO2

• Intermediate product of weathering• Highly pH dependent CEC = 5 - 350 cmol/kg• High S.A. = 70-300 m2/g

Al, Fe, Mn, Ti Oxides, Hydroxides, and Oxyhydroxides

• Weathering products of other minerals; Found in highly weathered soils

Fe oxides impart soil color (brown, yellow, red, orange, black)

• Often present as coatings on soil particles, in cracks, or as nodules

High surface areaFe and Mn oxides indicate redox

conditionspH dependent charge

• See Table 2.5 Sparks p. 60 for list of common oxide minerals in soils

http://soils.usda.gov/technical/classification/orders/images/oxisol.jpg

Oxisol – high in Fe and Al oxides

Microscopic view of an Inceptisol, showing small crystallites of carbonate minerals (around the central black void), quartz sand grains (white), and iron oxides and organic matter (dark brown).

http://www.britannica.com/ebc/art/print?id=19571&articleTypeId=0

csd.unl.edu

http://fr.wikipedia.org/wiki/Structures_cristallines_des_oxydes,_oxy-hydroxydes_et_oxydes_de_fer

http://fr.wikipedia.org/wiki/Image:Evolution2_wustite_hematite.gif

Carbonates and Sulfate Minerals

Calcite = CaCO3

Dolomite = CaMg(CO3)2

Siderite = FeCO3

Gypsum = CaSO4.2H2O

Soluble minerals (compared to silicates)Present in arid zones (high evapotranspiration)

Formed from precipitation out of solution as water evaporates

Rosettes of gypsum

Surface Area

• Specific Surface = the surface area per unit weight of material (m2/kg)

• Affects water retention and CEC

• Total S.A. = External surfaces + Internal (interlayer) surfaces

http://bio1151.nicerweb.com/doc/class/bio1151/Locked/media/ch06/06_07SurfaceVolumeRatio_L.jpg

http://www.gly.uga.edu/railsback/1121WeatheringArea.jpeg