8. Colloidal fraction

Question 1

colloidal fraction

Answer 1

Clay + humus particles

extremely small size-less than about 1 μm (0.000001 m)

colloid-like behavior.

Question 2

properties of colloids

Answer 2

Extremely small (<1 μm, sub-microscopic),
remain in suspension

• Plate-like, large external surface, sometimes high
  internal surface too.
• Surfaces typically charged (net negative):
  – Attraction / repulsion of each other
  – adsorption space for ions (exchange surface)

Question 3

4 types of soil colloids

Answer 3

– Crystalline silicate clays (less weathering, temperate)

– Allophane & assoc. non-crystalline clays (volcanics)

– Fe- and Al-oxide clays (most prominent in tropics)

– Humus (product of organic matter)