THE SOLID PHASE: BUILDING CONSTRUCTION MATERIALS AND PROCESSES

I. MAKEUP OF IGNEOUS ROCK (EXTRUDED)

ROCK TYPE GRANITE SYENITE GRANODIORITE DIORITE GABBRO DUNITE
REACTION ACIDIC a a a a BASIC
COLOR LIGHT a a a a DARK
MINERALS QUARTZ

ORTHOCLASE

BIOTITE

MUSCOVITE

HORNBLENDE

ORTHOCLASE

BIOTITE

MUSCOVITE

HORNBLENDE

ORTHOCLASE

Na PLAGIOCLASE

QUARTZ, BIOTITE

HORNBLENDE

MUSCOVITE

Na-Ca PLAGIOCLASE

HORNBLENDE

BIOTITE

Ca-Na-PLAGIOCLASE

AUGITE

OLIVINE

OLIVINE

AUGITE

MAGNETITE

CHROMITE

APPROX. % Si

>65

~65

65-60

55

50-45

~45

II. WEATHERING PRODUCTS

MINERAL RESIDUAL MINERALS RELEASED IONS
AMPHIBOLE CLAY MINERALS, LIMONITE, HEMATITE K, Ca, Mg, Na
BIOTITE CLAY MINERALS, LIMONITE, HEMATITE K. Mg
MUSCOVITE TENDS TO REMAIN, FINALLY ALTERING

TO CLAY MINERALS AND QUARTZ

K, SiO2 (COLLOIDAL?)
OLIVINE CLAY MINERALS, LIMONITE, HEMATITE Mg, Fe++
ORTHOCLASE

AND

MICROCLINE

CLAY MINERALS, QUARTZ. K, SiO2 (COLLOIDAL?)
PLAGIOCLASE CLAY MINERALS Na, Ca
QUARTZ QUARTZ SOME SiO2 (COLLOIDAL?)

III. STABILITY OF SOILS FORMING PRIMARY MINERALS: GOLDICH SERIES

IV. MINERAL WEATHERING SEQUENCE: JACKSON-SHERMAN WEATHERING STAGES

Characteristic minerals

in soil clay fraction

Characteristic soil chemical

and physical conditions

early stage

Gypsum, Carbonates, Sulfates, Soluble salts

Olivine/pyroxene/amphibole

Fe(II)-bearing micas

Feldspars

Very low content of water and organic matter

very limited leaching

Reducing environments

Limited amount of time for weathering

intermediate stage

Quartz

Dioctahedral mica/Illite

Vermiculite/chlorite

Smectites

Retention of Na, K, Ca, Mg, Fe(II), and silica:

    Ineffective leaching and alkalinity

    Igneous rock rich in Ca, Mg, Fe(II), but no Fe(II) oxides

    Easily hydrolyzed silicates

    Flocculation os silica, transport of Si into the weathering zone

advanced stage

Kaolinite, Gibbsite, Alophane

Iron oxides (goethite, hematite)

Titanium oxides (anatase, rutile, ilmenite), zircon, corundum)

Removal of Na, K. Ca, Mg. Fe(II), and silica:

    Effective leaching, fresh water

    Oxidation of Fe(II), acidic compounds, low pH

    Dispersion of silica, Al-hydroxy polymers

V. WEATHERING PROCESSES


An example: feldspar weathering (most abundant rock forming minerals on the earth surface)

1. Surface is hydrated

2. Surface Si-O-Al or Si-O-Si bonds are hydrolyzed, opening structure

3. Metal ion is released to solution (Additional protons balance charge)

4. A"metal leached" residual layer no more than 1.5 to 2.5 nm thick is created on feldspar surface.

5. Weathering reaches a steady state in which the leached layer dissolves at a rate equal to the rate of replacement of alkali metals by H+ at the interface between the leached layer and the intact structure.

(Items 2,3, and 4 represent nonstoichiometric weathering, 5 represents stoichiometric weathering)