What is meant by “ionic substitution” of elements in minerals, and how does this lead to variability in the compositions of some groups of minerals?

What is meant by “ionic substitution” of elements in minerals, and how does this lead to variability in the compositions of some groups of minerals?

Final Study Guide
The final exam will be comprehensive but will focus more on material covered since the last in-class exam. There will be a total of ~80 multiple choice questions, 40 from the first 2/3 of the course and 40 from the material we have covered since the last exam. It may include a few questions based only on the reading but will focus mostly on material covered in class. You may bring two 3×5 reference cards to the exam with you loaded with whatever information you think may be useful. In addition, as I explained in class, I will post a “word cloud” with most of the words appearing on the exam, and you may have an additional, 3rd card with definitions of any words that you are not familiar with. Good luck!
Outline of Topics covered by exam:
Part I
I. Minerals – Ch. 3
* Understand the different chemical bonds and their significance for the physical properties of minerals. For example, contrast diamond and graphite with respect to their crystal structure, the nature of the chemical bonds in each, and the following physical properties: hardness, cleavage, density, streak (i.e.,color of the powdered mineral), and luster. What gives diamond and graphite such different properties considering that they both consist of pure carbon?
* What is meant by “ionic substitution” of elements in minerals, and how does this lead to variability in the compositions of some groups of minerals?
* Cross out the three elements that do not belong in this list:
O, Si, Al, C, Mg, Fe, N, Ca, Na, K, H
What is the significance of the elements remaining on the list?
* What is the basic building block of the most abundant general family of minerals (the silicates)?
* Contrast the way quartz and olivine maintain charge balance in crystal structures based on complex ions of SiO4-4 (silica tetrahedra).
* Know which mineral is most abundant in the Earth’s mantle (olivine) and which minerals are most abundant in the Earth’s crust (i.e., quartz and the feldspar group).
* Name a mineral group that uses 6 of the 8 most abundant elements (hint: it is the most abundant group of minerals in the Earth’s crust — see above).
* What is the difference between chrysotile asbestos and the various types of amphibole asbestos. Why is the latter so much more hazardous?
* The most important group of minerals for engineers to understand are the clay minerals. What are the chief properties of the clay minerals? Strength? Compressibility? Permeability? Expansivity?
Understand their colloidal properties and how their colloidal behavior influences important engineering properties such as cohesion, impermeability, and plasticity.
Contrast the T-O structure of kaolinite with the T-O-T structure of montmorillonite and understand how these contrasting crystal structures influence the cation exchange capacities and especially the capacity to absorb and expand in interaction with water.
II. Igneous Rocks, Volcanism and Related Processes – Ch. 4
* What is the basis for the subdivision of the igneous rocks into volcanic (extrusive) and plutonic (intrusive). How are volcanic and plutonic rocks distinguished? (grain size)
* What is the basis for the subdivision of igneous rocks by compositional category (i.e., felsic, intermediate, mafic, and ultra mafic.
* Key igneous rock types to know: plutonic – peridotite, gabbro, diorite, granite; volcanic – basalt, andesite, rhyolite.
* What kind of igneous rocks are most abundant in the mantle? The oceanic crust? The continental crust?
* Be prepared to relate the major compositional categories of igneous rocks to plate tectonics and to the important process of partial melting. E.G., If oceanic crust is formed at mid-ocean ridges by partial melting of underlying mantle rock, then why is oceanic crust mafic rather than ultramafic in composition? (I.E., Relate to the fact that the melt is enriched in silica during partial melting).
* Be prepared to relate the formation of different types of igneous rocks to the plate tectonic environments in which they occur. ; subduction zones and arc volcanism – intermediate composition; continental settings such as rifts or continental hotspots – felsic).


 

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