SOIL 2124 EXAM 3 QUESTIONS AND
ANSWERS 100% PASS 2026/2027
Mineral or organic particles in soil having a diameter less than 1um (0.000001 m)- CLAY SIZE
RANGE - ANS Soil Colloid
Three types of clays - ANS Iron and aluminum oxide
non-crystalline silicate clays
crystalline and silicate clays
found in humid tropical climates, highly weathered, ultisols and oxisols
-some may have crystalline structure while others are amorphous - ANS Iron and Aluminum
Oxides
tightly bonded silicon, aluminum and oxygen NO ORDERED ARRANGEMENT
-volcanic ash, Andisols - ANS Non-crystalline Silicate Clays
DOMINANT IN MOST SOILS
-specific crystal structure - ANS Crystalline Silicate Clay
2 basic structural units of structured clays - ANS Si Tetrahedron
Al Octahedron
2026/2027 ALLRIGHTS RESERVED
1
,what makes a Sheet - ANS a series of structural units that are bonded together
what makes a Layer and two types - ANS Adjacent sheets that are bonded together
-1:1 (Si:Al), tetra:octa SiAl/SiAl
-2:1 (Si:Al), tetra:octa SiAlSi/SiAlSi
what makes a clay particle - ANS a series of layers
Where does permanent charge of clays come from? 1:1 or 2:1? - ANS isomorphous
substitution: the replacement of one atom by another of similar size in the crystal structure
2:1 clays
What is variable charge? 1:1 or 2:1? - ANS pH dependent charge
all except 2:1...1:1 clays, non crystall, silicate in Fe, Al oxides
-organic mater
-edges of clay (Si-OH)
What is the central atom in Tetrahedron and what is it replaced by? does it become more
negative or positive? - ANS Si4+
replaced by Al3+
becomes more negative
What is the central atom in Octahedron and what is it replaced by? more negative or pos? -
ANS Al3+
replaced by Mg2+
becomes more negative
1:1 silicates - ANS Kaolinite is most common
-halloysite, nacrite, and dickite
2026/2027 ALLRIGHTS RESERVED
2
, 2:1 silicates - ANS Illite, Chlorite, Vermiculite, Montorillonite
3 types if 2:1 silicates - ANS 2:1 non expanding
2:1:1 chlorite
2:1 expanding
Kaolinite - ANS 1:1
non-expanding
interlayer hydrogen bond (superglue)
large
NO ISOMORPH SUB, NO PERM CHARGE, surface charge is low
OCT-TET/H+/OCT-TET
Illite - ANS 2:1
non-expanding
three sheets per layer
interlater POTASSIUM K+, regular glue
ISOMORPH SUB
higher surface charge than kaolinite
TET-OCT-TET/K+/TET-OCT-TET
Chlorite - ANS 2:1
non-expanding
three sheets per later
Interlayer Mg OXIDE
ISOMORPH SUB
high surface charge
2026/2027 ALLRIGHTS RESERVED
3
ANSWERS 100% PASS 2026/2027
Mineral or organic particles in soil having a diameter less than 1um (0.000001 m)- CLAY SIZE
RANGE - ANS Soil Colloid
Three types of clays - ANS Iron and aluminum oxide
non-crystalline silicate clays
crystalline and silicate clays
found in humid tropical climates, highly weathered, ultisols and oxisols
-some may have crystalline structure while others are amorphous - ANS Iron and Aluminum
Oxides
tightly bonded silicon, aluminum and oxygen NO ORDERED ARRANGEMENT
-volcanic ash, Andisols - ANS Non-crystalline Silicate Clays
DOMINANT IN MOST SOILS
-specific crystal structure - ANS Crystalline Silicate Clay
2 basic structural units of structured clays - ANS Si Tetrahedron
Al Octahedron
2026/2027 ALLRIGHTS RESERVED
1
,what makes a Sheet - ANS a series of structural units that are bonded together
what makes a Layer and two types - ANS Adjacent sheets that are bonded together
-1:1 (Si:Al), tetra:octa SiAl/SiAl
-2:1 (Si:Al), tetra:octa SiAlSi/SiAlSi
what makes a clay particle - ANS a series of layers
Where does permanent charge of clays come from? 1:1 or 2:1? - ANS isomorphous
substitution: the replacement of one atom by another of similar size in the crystal structure
2:1 clays
What is variable charge? 1:1 or 2:1? - ANS pH dependent charge
all except 2:1...1:1 clays, non crystall, silicate in Fe, Al oxides
-organic mater
-edges of clay (Si-OH)
What is the central atom in Tetrahedron and what is it replaced by? does it become more
negative or positive? - ANS Si4+
replaced by Al3+
becomes more negative
What is the central atom in Octahedron and what is it replaced by? more negative or pos? -
ANS Al3+
replaced by Mg2+
becomes more negative
1:1 silicates - ANS Kaolinite is most common
-halloysite, nacrite, and dickite
2026/2027 ALLRIGHTS RESERVED
2
, 2:1 silicates - ANS Illite, Chlorite, Vermiculite, Montorillonite
3 types if 2:1 silicates - ANS 2:1 non expanding
2:1:1 chlorite
2:1 expanding
Kaolinite - ANS 1:1
non-expanding
interlayer hydrogen bond (superglue)
large
NO ISOMORPH SUB, NO PERM CHARGE, surface charge is low
OCT-TET/H+/OCT-TET
Illite - ANS 2:1
non-expanding
three sheets per layer
interlater POTASSIUM K+, regular glue
ISOMORPH SUB
higher surface charge than kaolinite
TET-OCT-TET/K+/TET-OCT-TET
Chlorite - ANS 2:1
non-expanding
three sheets per later
Interlayer Mg OXIDE
ISOMORPH SUB
high surface charge
2026/2027 ALLRIGHTS RESERVED
3
