Geologic definition: Loose surface of the earth as distinguished from solid bedrock or

Soil

Material which nourishes and supports growing plants (includes rocks, water, snow, air).

Soil Mixture of inorganic matter (mineral), organic

matter, water, and air.

Organic Matter

original tissue—twigs and leaves on forest floorhumus—rich brown color in soil decomposed materialAs organisms die, they are attacked by microorganisms: fungi, bacteria, and others.

% Soil components varies:

• Type of vegetation

• Amount of mechanical compaction

• Amount of soil water present.

Soil Formation

Why do we study soil? Because It’s A(n)

Great integrator

Producer andabsorber of gases (CO2 and others)

Medium for plant growth

Medium of crop production

Home to organisms(plants, animals and others)

Waste decomposer

Snapshot of geologic, climatic, biological, and human history

Source material for construction, medicine, art, etc.

Filter of water and wastes

Essential natural resource

Medium of heat andwater storage

Well-drained

Poorly drained

Weathering forces

• Rocks & minerals break down smaller pieces

– Temperature changes

– Water action

– Plant roots

– Ice expansion

– Mechanical grinding

Temperature changes—heating and cooling of rocks can cause rock to crack into smaller pieces.

Water action--Water soluble minerals dissolve when exposed to water. Some rocks may contain some minerals that are water soluble and only that part of the rock will dissolve

Plant roots—Roots of plants growing in cracks in rocks can widen cracks and break rocks apart.

Ice expansion—If a rock has a crack that can fill up with water, when the water expands when it freezes. This can break rock into smaller pieces.

Mechanical grinding—wind blowing sand across rocks, or glaciers grinding rocks against each other. Example—rock tumbler

Blocky

PlatyGranular

Clay Mineralogy

• Clay is a particle SIZE

• Predominant make-up is minerals

1. Silicate Clays (aluminosilicates)

Composed of tetrahedral and octahedral “sandwiches”

Tetrahedron: central cation (Si+4, Al+3) surrounded by 4 oxygens

Octahedron: central cation (Al+3,Fe+2, Mg+2) surrounded by 6 oxygens (or hydroxyls)

tetrahedron

octahedron

• 1000s of tetrahedra and octahedra connect in clay minerals to give:

– Planes of Si, Al, Mg

– Planes of Oxygen, hydroxyl groups

• Sheets combine to form layers

• Layers are separated by interlayer space

– Water, adsorbed cations

kaolinite

kaolinite

Scanning Electron Microscope image

Montmorillonite

Illite

DENSITY INDEX OR RELATIVE DENSITY

• The density index is defined as,

ID = (emax – e / emax – emin)

Where,

emax = void ratio in the loosest state

emin = void ratio in the densest state

e = natural void ratio of the deposit

• This term is used for cohesion less soils only.

• When the natural state of the cohesionless soil is in the loosest form,

emax= e.