Slide 1 Flashcards
What are the major types of clay soil?
Kaolinite, Illite, Montmorillonite
These types are of primary interest from an engineering perspective.
What is the basic mineralogical structure of clays?
Clay minerals are composed of two basic units:
* Silica tetrahedron (Si4O10)4−
* Alumina octahedron (Al2(OH)6)
These units are held together by ionic bonds.
What is cation exchange capacity (CEC)?
The maximum mass of all cations that a soil can attract and hold for exchange with the soil solution
CEC is expressed in milliequivalent (meq) of hydrogen per 100 g of dry soil.
Fill in the blank: The most common soil cations include calcium (Ca++), magnesium (Mg++), potassium (K+), ammonium (NH4+), hydrogen (H+), and _______.
sodium (Na+)
These cations are essential for soil health and nutrient availability.
What is isomorphous substitution in clay minerals?
The substitution of an atom or ion in the tetrahedral or octahedral positions of clay minerals by other atoms or ions of similar size without changing the crystal structure
This process increases the negative charge on the particles.
True or False: Silicate minerals make up about 90% of the rock-forming minerals of the earth’s crust.
True
Silicate minerals significantly influence the properties of clay soils.
What happens when rocks and water come into contact?
Clays are produced
The reaction involves minerals like feldspar undergoing chemical weathering.
List the minerals from most reactive to least reactive.
Olivine, Ca-feldspar, Pyroxene, Amphibole, Na-feldspar, Biotite, K-feldspar, Muscovite, Quartz
This order reflects their susceptibility to weathering.
What is the structure of quartz?
Tectosilicates, forming a 3-D lattice structure
Quartz is very strong and not easily susceptible to chemical weathering.
What is the significance of specific surface in clay minerals?
It is the surface area of the clay mineral per unit weight or mass
Higher specific surface results in greater surface forces of attraction and repulsion.
Fill in the blank: The innermost layer of double layer water, held strongly by clay, is known as _______.
adsorbed water
This water is more viscous than free water.
What is the relationship between water and clay particles?
Water molecules are attracted to the negatively charged surface of clay particles
This interaction is influenced by the dipolar nature of water.
True or False: The octahedral units consist of six hydroxyls surrounding an aluminum atom.
True
The octahedral unit can also include magnesium and other cations.
What defines a mineral?
A chemical compound formed in nature during a geological process
Minerals differ from rock fragments, which consist of a combination of minerals.
What is the role of hydrogen ions in the formation of clay from feldspar?
Hydrogen ions displace cations from feldspar, transforming it into kaolinite
This reaction also results in the dissolution of silica.
What are the two types of bonding in clay minerals?
Primary bonding (intersheet) and Secondary bonding (interlayer)
Secondary bonding includes hydrogen bonding and van der Waals forces.
What is the general formula for feldspars?
Si3O8
Feldspars are tectosilicates that form a 2-D lattice structure.
What are the two basic units in clay minerals?
Silica tetrahedron and Alumina octahedron
These units combine to form the structure of clay minerals.
What happens to cation concentration in the diffuse double layer?
Cation concentration decreases with distance from the surface of the particle
This is due to the force of attraction between water and clay decreasing with distance.
What are the three clay minerals of interest from an engineering point of view?
Kaolinite, Illite, Montmorillonite
What consists of repeating layers of elemental silica-gibbsite sheets in a 1:1 lattice?
Kaolinite
What is the basic unit structure of kaolinite?
A two-layer unit formed by stacking a gibbsite sheet on a silica sheet
What holds the layers of kaolinite together?
Hydrogen bonding
What is the thickness of each layer in kaolinite?
7.2 Å (0.72 Nm)
