Clay Minerology Flashcards
Why are phylosilicates considered to be so important?
They are one of the most common mineral groups. Along with organic colloids, clays provide “storage sites” for critical plant nutrients.
What problems can result from mistreatment of clays in soil?
Compaction - Puddling
-results in reduced water infiltration capacity, reduced rooting potential, erosion and loss of soil productivity.
In what group of rocks are phyllosilicates most common?
Sedimentary rocks including mudstone, claystone and shales (about 40% of sed. rocks are clay minerals)
Why are clays an important aspect of engineering?
Some clays expand when exposed to water, causing major stability issues that must be calculated before constructing roads…
What are clays of northern latitudes generally produced from?
Silicate RFM’s (specifically feldspars)
Describe the basic structure of phyllosilicates.
based on interconnected rings of 6 silica tetrahedrons that extend out in sheets. 3 out of 4 oxygens from each tetrahedra are shared between the ring, leading to a basic structure of Si205(-2).
What is the formula for a Silicon tetrahedra?
What about a basic ring of Silicon tetrahedra?
Silicon tetrahedra - Si04(-4)
Ring - Si205(OH)(-3) Since there is usually an OH ion in the center of the ring.
In clays, what do the tetrahedral sheets bind to?
octahedral sheets formed from small cations like aluminum or magnesium surrounded by 6 oxygen atoms.
What are the 3 main clay groups and what are their layer ratios?
give examples of specific types of clay in the groups.
Kandite - 1:1 clay (Kaolinite is most common) Al2Si205(OH)-4 - formed from the weathering of feldspars.
Smectite - 2:1 clay (Montmorillonite is most common) Expansive clay formed from the weathering of volcanic ash.
Illite - 2:1 clay (non expansive) - formed from weathering of K and Al rich rocks.
How is Kaolinite formed?
weathering of aluminosilicate minerals, (rocks rich in feldspar). In order to for kaolinite to form, other ions like K, Ca, Mg and Fe must be leached first, therefor kaolinite forms well in acidic conditions with granitic rock types.
What is mixed layer clay?
consists of clays that change from one type to another in a stacking sequence that can be regular or irregular.
How can you distinguish clay minerals?
Clay minerals are so small that they cannot be easily distinguished by hand. Expansive clays can be identified by the eating test which can tell you if it is either a smectite or one of the other two types. X ray techniques are required to accurately identify clay minerals as a function of stokes law.
What is a type of 2:1:1 clay?
Chlorite.
What are clay minerals also referred to?
Phyllosilicates
