Most questions for the lecture tests will come verbatim or nearly so from these questions. You just don’t know which ones I will pick. You may ask the instructor at any time prior to tests if you are getting answers correct. This is to be used primarily as a study tool. If you use it soon after a lecture, you will usually be able to get much more of the correct info into your answers than if you wait several days or until the night before the test.

1. Be able to write a statement (of a few sentences) that distinguishes a mineral from an element and from a rock, and that relates elements, minerals, and rocks.

2. What are the two main factors that define a mineral according to our present strict definition of a mineral?

3. When we speak of a mineral’s “crystal structure”, to what are we referring?

4. If a mineral’s chemical formula is given (for example for pyrite, FeS₂) explain what the Fe, the S, and the subscript 2 mean.

5. If a mineral grows unhindered, the shape that the mineral will take on is primarily influenced by what?

6. What do the terms euhedral, subhedral, and anhedral mean in describing a mineral occurrence?

8. What two factors may contribute to one mineral having higher density than another?

9. If one measures density as grams per cubic centimeter, which statement is correct? ______

11. On an atomic scale, what is it that gives one mineral a greater hardness than another?

12. I might give a question asking what hardness number is represented by apatite_____? By quartz_____, etc. Or “which is harder, gypsum or fluorite?” (i.e. learn the Mohs hardness scale!).

15. Does the presence of a particular element in minerals consistently impart a particular characteristic color for all the minerals that have that element?

Lecture #2, Tuesday, 8/29/06–Basic Chemistry Review

1. Be clear regarding the distinction between what defines a neutral atom, an ion, and an isotope. Also be clear what (on an atomic level) defines an element [i.e. the number of protons]. Be able to answer questions something like these:

"Atom" A has 126 neutrons, 82 protons, and 80 electrons

"Atom" B has 127 neutrons, 83 protons, and 80 electrons

_____Which if either is a neutral atom?

_____ Which if either is an ion?

_____ Are these isotopes of the same element?

_____ Do these “atoms” represent the same element or different elements?

2. Know the chemical symbol for the elements I indicated in class (in a table in handout)

3. Of the three man “building blocks” of an atom (protons, neutrons, electrons), which aspect of atoms is responsible for chemical behavior?

4. Of the three man “building blocks” of an atom (protons, neutrons, electrons), which aspect of atoms is responsible for most of the mass of the atom (most of the “weight”)?

5. Between “cation” and “anion”, be sure to know which means a positive ion and which means a negative ion.

6. What kind of electron cloud configuration is typical of the “noble gases”?

7. In the periodic chart of the elements, the integer number that is given refers to___

d) the order in which the elements were discovered, the first being hydrogen, the second helium, etc.

8. Know the common charge found on typical ions in earth materials–also which elements commonly have variable oxidation state in nature (this was in a handout).

10. In the periodic chart of the elements, how are elements that have similar chemical behavior arranged?

11. In the periodic chart of the elements, how are elements that have similar configuration of their electron cloud arranged?

12. Considering a single atom, what is more important to that atom, maintaining charge balance between its nucleus and electron cloud, or obtaining a noble gas configuration in its electron cloud?

13. Two minerals have iron in their formula. Mineral A is said to have ferric iron and mineral B has ferrous iron. What is the specific difference between the iron in these two minerals?

Lecture 3. Thursday, 8/31/06—Chemical Bonding in Minerals

1. Which bond type is a result of electrostatic attraction?

2. Describe briefly how an ionic bond works.

[Note: this is essentially the flip side of the previous question, but I would want a more detailed answer than just “electrostatic attraction”. You would want to convey that in order to obtain a more stable configuration some elements give up electrons and become positively charged ions and others gain electrons and become negative ions, then the positive and negative ions are attracted by electrostatic forces and are thus bonded.]

3. Which bond type is characterized by atoms sharing electrons, with parts of their electron clouds interpenetrating and shared electrons being attracted to both nuclei?

4. Describe briefly how covalent bonds work. [This is flip side of question 3].

5. Which bond type has atoms packed together with a cloud of mobile valence electrons moving among them?

6. Describe briefly how metallic bonds work. [This is the flip side of question 5.]

7. Which bond type (or types) tends to give rise to minerals that are relatively soluble in water?

8. Which bond type is common in the hardest minerals?

9. Which bond type tends most to promote electrical conductivity?

10. Which is a stronger “force” in controlling an atom’s behavior?

a) maintaining electric neutrality in the atom

b) obtaining a stable electron cloud configuration

11. What are the two weakest bonds, giving rise to minerals with very low “hardness”?

12. Be able to use the example of diamond and graphite to illustrate in a brief discussion how some minerals may have the same bond type throughout its crystalline structure while other minerals can have different bond types within the same crystal.

13. Why is it that a mineral like galena (PbS) has some physical properties that are characteristic of metallic bonds (for example, metallic luster) and other properties characteristic of ionic bonding (for example, brittle breakage instead of malleability)?

14. In many minerals we are dealing with atoms that behave for the most part as charged ions, some being cations and some being anions. However, in quite a few, such as calcite, CaCO₃ we consider part of the composition as an “anionic radical”, rather than just speaking of anions. In calcite, which part composes the anionic radical, and what makes it a radical?

Lecture 4. Tuesday, 9/5/06

1. What bonding type characterizes the minerals gold, silver, and copper?

2. What is the term for the style of packing of atoms in minerals composed of one element, in which the bonding between atoms is of the metallic bond type? (Actually there are two variations in this basic style)

3. Regarding the style of packing of atoms in metallically bonded minerals, how does this style relate to typical densities of such minerals?

4. Gold (Au) and silver (Ag) are often amalgamated in nature. This occurs because…________.

a) the atomic radius of Au is close to that of Ag

b) the common ionic charge of Au is close to that of Ag

c) the common ionic charge of Au is the same as that of Ag

d) the atomic number of Au is close to that of Ag

5. Which chemical bond type has a strong influence on where adjacent atoms must be positioned with respect to each other in a crystal, the positions being compatible with the orientations of electron orbital shapes?

6. What factor below governs the way anions pack together with cations (i.e. how they coordinate in the crystal structure) in ionically bonded minerals?

a) They pack together in arrangements governed by their relative sizes

b) They pack together in arrangements governed by their relative charges

c) They pack together in arrangements governed by their atomic number

d) They pack together in arrangements governed by the column in which they occur on the periodic chart of the elements

7. Typically a cation is (smaller than, larger than, equal to) the size of the equivalent neutral atom. [Circle correct answer]. Same question could be for “anion”.

8. If an element has multiple valence states, such as hypothetical element X (X⁴⁺ and X³⁺). Which of the two should have a smaller ionic radius?

[Note: I forgot to mention this in class, but you should be able to figure it out based on a principle we did discuss. That is, the one with more positive charge will be smaller because it has a greater proportion of positive charge in the nucleus relative to the net negative charge in the electron cloud. The typical example in nature is iron, where Fe³⁺ is a little smaller than Fe²⁺.]

9. In general, which tend to be larger, cations or anions?

10. If cation A is larger than cation B, it is most likely that A will have a ___________(larger, smaller) coordination number than B.

11. Know the most common coordination number of the following cations with oxygen in typical silicate minerals. Be sure to remember the two common coordination numbers of Al.

Si, Al, Fe, Mg, Ca, Na, K

12. Know the coordination polyhedrons associated with the following coordination numbers.

3, 4, 6, 8, 12

13. Which factor (or factors) below is (are) true factors that influence how ionically bonded elements become arranged when they are attracted by electrostatic forces. (Circle correct).

a) anions draw close to cations and tend to touch one another (anion touching cation)

b) anions draw close to anions and tend to touch one another (anion touching anion)

c) cations draw close to cations and tend to touch one another (cation touching cation)

d) cations repel anions and become arranged so that they never touch each other

e) cations repel cations and become arranged so that they never touch each other

f) anions repel anions and become arranged so that they never touch each other

14. We often speak of a “site” in a crystal structure where a particular element resides in the structure. By what phenomenon in crystal structures are “sites” usually identified? [We identify them by their coordination number or the coordination polyhedron, such as a “tetrahedral site” or a “4-fold coordination site”.]

15. In what way are adjacent coordination polyhedra in a crystal structure linked? [They are linked to each other by sharing apices. That is, adjacent polyhedra will share the apical ions. They can share one apex, two apices, or in some cases three.]

1. If two minerals are said to be “isostructural”, what are we saying about these two minerals?

[The answer to this question should mention something about the chemical composition and about the crystalline structure.]

2. If two specimens are identified as having the same crystalline structure, but different elements involved, are they the same mineral or different minerals?

3. What is the difference between “isostructuralism” and “polymorphism”?

4. If two specimens are found to have the same chemical composition, but the arrangement of the atoms involved is different, are these two the same mineral or different minerals?

5. Be able to explain the basic difference between any of the three types of polymorphism [i.e. reconstructive, displacive, and order-disorder polymorphism].

[Note: this is basically just being able to say that reconstructive polymorphism is where two polymorphs have entirely different structures; whereas displacive polymorphism is where two polymorphs have similar structures, but slight bond-length issues cause the two to have different symmetries and thus are considered different structures; and finally order-disorder polymorphism is where the structures are basically the same, but certain elements are either ordered in where they reside in the structure (regularly repeated position), or they are disordered as to where they reside.]

6. If one polymorph is denser than another, which of the two is normally favored by high pressure, the denser or the less dense one? Which is favored by high temperature?

8. Of the three different types of polymorphism, which requires the least time and energy in order for a polymorphic transformation to take place? Which requires the most? [From the class discussion, it should be evident that order-disorder polymorphic transformation requires more time and energy to be accomplished than displacive, but less than reconstructive polymorphic transformation.]

9. Which of the three different types of polymorphism is thought to possibly require some kind of catalyst in order for the polymorphic transformation to take place?

10. What kind of polymorphic relationship is there between a-quartz and b-quartz?

12. In what kind of geologic situation can we find crystals in the shape of b-quartz?

13. With regard to the type of polymorphism involved in the K-feldspar polymorphs, what is the difference b/t sanidine, orthoclase and microcline?

[Because the question asks “with regard to the type of polymophism”, the difference has to do with the degree to which each mineral is “ordered” vs “disordered”. It would be sufficient as far as I am concerned if you could point out that in sandine the position of Al in the crystal structure is completely unordered (randomly distributed among tetrahedral sites), whereas in orthoclase there is partial ordering, and in microcline the Al is totally ordered (resides only in one repeated tetrahedral site in the structure). ]

14. Regarding sanidine, orthoclase, and microcline, know which is the high temperature form, which is the intermediate temperature form, and which is the lower temperature form.

15. With regard to their occurrence in igneous rocks, in what setting do we normally find the K-feldspar polymorphs?….

16. Be able to answer an essay question regarding the geologic setting in which we normally find sanidine vs orthoclase vs microcline–explain WHY we find them in the respective settings, in terms of polymorphic transformation.

[Note: it is highly likely that I will ask this on a test. I highly recommend that you write out an answer now and show me so I can tell you if you are covering the question correctly and sufficiently thorough.]

Lecture 6. Tuesday, 9/12/06

1. What is the basis of the classification system of minerals that is used today?

2. The chemical composition of minerals has been chosen as the basis of classification among minerals. What in particular about the chemical composition is the key to the classification system?

[Remember I told you at the beginning that some questions may have overlap and some may go at the same thing from different angles. Obviously I would not have both #1 and #2 on the same test.]

4. In the case of “substitutional” solid solution, what governs whether or not two particular elements can substitute for one another? (What must they have in common?)

5. What is the difference between “complete solid solution” and “limited solid solution”?

6. What is “coupled substitution” and why does it occur in some minerals? [Note: your answer must clearly indicate that ions of similar size may substitute even if the charge value is different and explain how a coupled substitution solves the problem of charge imbalance.]

7. Name a mineral species in which coupled solid solution is important and what elements are substituted.

8. What is “interstitial solid solution”, and how does it work? Name one species of mineral that has this kind of solid solution.

9. For industrial uses of the element cesium (Cs) one source for the element is the mineral beryl. Explain why Cs can occur in variable amounts in the mineral beryl. [This question is similar to #8. I would like you to comment that Cs is a large cation and that there are large open sites in the beryl structure in which the Cs can lodge.]

10. What is “omission solid solution”, and how does it work? Name one species of mineral that has this kind of solid solution.

11. In ideal pyrrhotite, a 1 to 1 ratio occurs between iron (Fe) and sulfur (S). In this ideal situation, the Fe is Fe²⁺ and the S is S^2-. In “real life” of the earth’s environment some of the Fe is oxidized to Fe³⁺. How does pyrrhotite handle the charge imbalance that is produced? [Note that this is similar to question 10, but from a different direction.]

12. Be familiar with the use of (…. ) in writing mineral chemical formulae where solid solution is involved. Know the situation for which a comma is put and any subscript is outside the parenthesis, and the situation for which there is no comma used and subscripts do occur inside the parenthesis.

14. A journal article states that a sample of olivine from a particular location is Fo₄₂Fa₅₈. What is being said about this olivine?

2. For a crystal to be stable, what relationship is best regarding the surface/volume ratio of the entire crystal?

3. Are tiny crystals generally more stable than large crystals in an environment of potential crystal growth? Or vice versa?

4. Is a crystal’s surface in general stable or unstable as compared to interior? Why?

5. Basically what is the “nucleation problem”? [Note this question touches on aspects of the questions above.]

7. During growth, what with respect to lattice planes (i.e. planes in the crystal structure) characterizes faces that tend to grow fast?

8. During growth, what with respect to lattice planes characterizes the most stable faces?

9. During early growth, which kind of faces tend to be most commonly present, faces on lattice planes of low atom density (few atoms/unit area) or faces on lattice planes of high atom density?

10. During later growth, which kind of faces tend to be most commonly present, faces on lattice planes of low node density or faces on lattice planes of high node density?

11. What part of a crystal’s 3-D lattice tends to grow prominently to form dendritic crystals?

12. Does dendritic growth tend to result from conditions of slow growth or from fast growth or from neither?

14. When chemically zoned crystals of a solid-solution mineral grow from an igneous melt, there is a common relationship between the composition of the core and the composition of the rim. What is that common relationship? Hint: has to do with melting point.

Lecture #8. Tuesday, 9/19/06

Note: After posting on Tuesday, I later added a few questions to this day's study questions

1. In your own words describe how chemical zoning takes place in some solid solution minerals growing in an igneous melt.

[This would be a longer answer mainly pointing out that whatever the ratio of two solid solution end members there is in a melt, the first crystals that form will be enriched in the high-temperature end member as compared to their proportions in the melt. Consequently the remaining melt will be somewhat depleted of the high temperature end member and enriched in the low temperature end member. Therefore the next layer that adds on will have a composition with a little lower proportion of the high temperature end member than the first layer, and so on.]

3. Although we used plagioclase to illustrate chemical zoning, its zoning behavior is very critical to understanding a number of phenomena in igneous rocks. The following question can be gleaned from that discussion and should be remembered. Q: When plagioclase occurs as a normally zoned crystal, the core is typically _____ and the rim is typically _____.

4. “Equilibrium crystallization” generally takes place under_____ conditions.

5. ______Which statement below would describe the chemical composition situation of a solid solution mineral crystal that grew under equilibrium crystallization conditions?

For the next lecture exam, be ready for the kind of questions given in the handout on reading the plagioclase phase diagram

Lecture #9. Thursday, 9/21/06

1. It is not uncommon to find minerals of two different species intergrown because two individual crystals began to grow toward each other, and they grew until the two grew into each other. It is also possible to find many cases where two crystals of the same mineral species are intergrown for the same reason. However, “twinning” intergrowth is a different phenomenon. What about “twinning” intergrowth is the key to recognizing that this intergrowth is from twinning and not just a chance occurrence?

[Basically there were two matters in how we defined twinning in class that would apply here.]

3. Know the difference between the 4 twinning styles–simple (contact) twins, polysynthetic twins, cyclic twins, and penetration twins.

4. What style of twinning is the most common twinning seen in plagioclase?_______

What is the name given to this twinning in plagioclase?____________________________

[Note that I could ask a question that ties in concepts of Q.3 and Q.5–for example “Describe the difference in the disposition of twin composition planes in contact twins vs polysynthetic twins”, or “Describe the difference in the disposition of twin composition planes in polysynthetic twins vs cyclic twins”, etc.]

6. What mineralogically is the actual thing that is expressed as “striations” seen on certain cleavage surfaces of plagioclase of crystals?

7. What are three processes in a mineral’s “history” that could produce some form of twinning?

8. Name a common mineral that is usually characterized by having twins developed by polymorphic transformation twinning, and what do those twins look like?

Lecture #10, Tuesday, 9/26/06

1. Does recrystallization tend to make crystal boundaries smoother or more irregular?

2. Does recrystallization usually make crystal grain size decrease or increase?

3. Recrystallization is typically takes place as a result of [lowering, increasing] temperature.

4. Recrystallization is basically a processes that operates to [increase, decrease] the surface/volume ratio of the crystals.

5. T, F --Recrystallization involves melting of mineral crystals and then new ones growing.

6. Know what pseudomorphism is and how it comes about. Know the example of pyrite replaced by goethite.

7. How can the phenomenon of pseudomorphism aid geologists in determining what minerals occurred in a rock prior to metamorphism?

[We were kind of hurrying here. In metamorphism of relatively “low grade” (not too high a temperature) and if there are little or no deformational stresses going on, the new, metamorphic minerals that grow due to the increased temperature may grow in such a way that the new minerals replace the original ones “pseudomorphically”. Consequently original rock textures may be preserved that may be useful in the “detective” work of figuring out what kind of rock it was before metamorphism.]

8. What is "saprolite" and what does it have to do with pseudomorphism?

[Again, we were going fast here. This case is similar to the one above. “Saporlite” (=”rotten rock”) is the weathering products of the minerals that originally formed a rock having replaced those original minerals pseudomorphically and thus preserving textures characteristic of the original rock prior to weathering. It tends to occur in the “C-horizon” of the soil profile, especially from weathering of igneous and metamorphic rocks.]

9. What basically is “exsolution” in minerals?

10. Which does higher temperature tend to favor–a more complete solid solution series or a more limited series?

11. Exsolution is more likely to take place under _____ conditions.

a) rapid heating

b) slow heating

c) rapid cooling

d) slow cooling

12. Exsolution is more commonly observed in minerals that occur in _____. Explain why.

a) plutonic igneous rocks b) volcanic igneous rocks

[Note that we did not discuss this explicitly, but the same concept as in question #11 above is involved. You should be able to figure this out. See me if you are having problems.]

13. Explain the role of “complete solid solution” vs “limited solid solution” in the matter of exsolution.

14. Explain what takes place on an atomic level in order for exsolution to take place.

16. It is possible for inclusions of one mineral to occur in another host mineral if the included mineral grew first and then the host mineral grew around the pre-existing mineral. Inclusions can also form from the process of exsolution. How can we distinguish inclusions formed by exsolution from inclusions formed by some other process?

[Answer should point out the fact that an exsolved mineral tends to line up with crystallographic planes in the host, rather than just being of random orientation.]

Lecture #11. Thursday, 9/28/06

1 . What is meant by the term “polymerization” with respect to the silicate minerals?
[Note: Your answer must point out that it is direct linking of Si-O tetrahedra in a crystal structure. Don't just say linking of Si in the structure. That would be incorrect.]

2. What is a “bridging oxygen” in the discussion of polymerization in silicate mineralogy?

3. Describe the polymerization style of the chain silicates (and point out the two subgroups under his heading).

[This question could be asked for any of the silicate groups: orthosilicates, disilicates, ring silicates, chain silicates, sheet silicates, framework silicates (except these would not have the two subgroups). If I ask for ring silicates, don't forget to mention rings may be of 3, 4, or 6 Si-O tetrahedra. Also the note in question 1 applies here as well.]

4. To what silicate group do the pyroxenes belong? The amphiboles? (Be specific as possible.)

5. To what silicate group do the micas belong? In what way does the polymerization style of that group influence the cleavage phenomenon in the micas?

[NOTE: An important point to keep in mind is that the Si-O bonding in the silicates is the strongest bond in the structure. Since the micas belong to the sheet silicates, within the sheet there are strong bonds; but between the sheets there are other bonds that are weaker, hence cleavage in one direction. ]

Correction!!! We need to include the remainder of this lecture on the 2nd Lecture Test -- even up through Opal on Tues 10/3 lecture

Thursday 9/28/06 -- CONTINUED

Important Minerals in Geology – SiO₂ Minerals

6. If I list a number of mineral names, be able to pick out which are polymorphs of SiO₂.

7. Of the following polymorphs of SiO₂, be able to identify which are more directly associated with high temperature of formation, and which of high pressure:

stishovite, coesite, tridymite, cristobalite, α-quartz, β-quartz.

High Temperature______________________________________

High Pressure__________________________________________

[Note: I list α-quartz here only as a “red herring”. It is the polymorph that remains stable at the earth’s surface conditions. I would like you to remember that β-quartz, tridymite, and cristobalite are high temperature forms, and that coesite and stishovite are high pressure forms.]

8. What kind of geologic situation is a typical occurrence of the mineral coesite?

[I mention this in class briefly. Coesite has been found as tiny inclusions in diamond. In the lab, both coesite and diamond are found to have high pressure stability fields—pressures that occur in the earth only at depths of the mantle, the probable origin of diamonds. Also coesite has been found at meteorite impact sites, where quartz in sandstone was converted almost instantaneously to coesite and to stishovite. I don’t know how this could happen so fast, unless the crystals are extremely small.]

9. What kind of geologic situation is a typical occurrence of the mineral stishovite?

10. How do we recognize that β-quartz occurred in certain volcanic rocks when the mineral first crystallized? Why is it that we always find that the β-quartz has inverted to α-quartz?

11. Why are some quartz occurrences with clear quartz and some are colored varieties? (That is, what makes the difference in color?)

[Ans: Various impurities can occur in the quartz, imparting different colors.]

12. What is it that makes “milky quartz” look “milky”? What is the typical geologic situation in which milky quartz is found?

14. What properties does covalent bonding impart to quartz that makes it so resilient in the environment of the earth’s surface, so that we find it in great abundance in various sand deposits in rivers and beaches? [Remember that there are two factors.]

16. Distinguish the microhabit of chalcedony and chert. That is, what is the difference in their habit on a microscopic scale?

17. What is the typical geologic occurrence of chalcedony? (Name two situations of occurrence.) [Did I tell you in class?—(1) low-T hydrothermal veins, fillings in various cavities in rock such as gas vesicles in volcanic rocks or fractures. (2) petrified wood.]

18. What is the typical geologic occurrence of chert? (Name two situations of occurrence.)

1. Opal is considered to be a mineraloid and not a true mineral by modern definition. In what way does opal fit the requirements for being considered a “mineral”, and what about opal disqualifies it from being truly a “mineral”?

THE REMAINDER OF THE LECTURE OF THIS DAY WILL NOT BE TESTED UNTIL THE THIRD LECTURE TEST.

2. What kind of rocks are host to the famous “Mississippi Valley type” ore deposits?

3. What is considered to be the origin of the ore‑depositing fluids that formed “Mississippi Valley type” ore deposits?

[This should be a basic description of the orogenic belt in which the high elevation drives ground water deeply and laterally to emerge at lower elevation. This water leaches elements, including the economic ones, out of a large body of rock that it flows through, making an ore-depositing fluid that precipitates ore minerals in the shallower zone near its discharge point.]

4. Considering the concept of a natural process that operates to concentrate normally rare elements, how does this concept apply to “Mississippi Valley type” ore deposits?

[This should be a description of the small quantities of rare elements being leached out of a large volume of rock throughout the orogenic belt that eventually seep through shallower rock to precipitate economic minerals in fractures or other voids in a relatively small area (therefore , the concentration has greatly increased).]

5. Can Mississippi Valley type ore deposits be found in Arkansas? If so, in what part?

6. What are the economic minerals in the primary ore that are most commonly associated with “Mississippi Valley” type ore deposits? And what are the elements that are extracted for economic use?

7. In the kind of system that most geologists believe to be the origin of Mississippi Valley type ore deposits (such as we discussed in class), what is it that makes the hydrothermal waters that deposit the ore to be hot?

The next questions are about the supergene enrichment process we discussed in class. We discussed this process with regard to sulfide ore deposits in general, not to the Mississippi Valley deposit specifically, although we pointed out how aspects of the full process apply to the Rush ore deposit we saw.

8. In the supergene enrichment processes, how does a “gossan” form? Include what original mineral it comes from and what mineral is it primarily made of now.

10. In the case of a sulfide ore deposit with chalcopyrite as a major primary ore, where in relation to the water table is the “zone of sulfide enrichment”?

11. Which of the following minerals is typically precipitated in the “oxidized zone” of a sulfide ore deposit?_______

12. In the supergene enrichment process, how does pyrite play a role in making the water more reactive?

1. I would like you to be able to write an essay-type answer about the basic principles of pluton-related hydrothermal systems. Include in your answer--

ü What drives hydrothermal circulation (note this goes hand in hand with previous)

ü The concept of how this system is a natural process that can concentrate gold or other economic elements (Note that the Au and other elements are in low concentration over a large area prior to the process occurring. The elements are leached out of the large area and as pass through small areas of proper chemical conditions where they precipitate out as economic minerals in restricted zones such as in veins or on the surface as a volcanogenic exhalative.)

2. What are the most typical kind of “metamorphic reactions” that occur in regional metamorphic settings and what do they have to do with some hydrothermal deposits? Write a brief but informative discussion of the basics of a hydrothermal system in a metamorphic setting. Be sure to include the concept of how this system is a natural process that can concentrate gold.

4. Gold can be found in some places in volcanogenic exhalative deposits. What other kinds of economic minerals in some situations occur in this kind of deposit?

5. If you were told that gold is all over the top of a sand bar in a creek, why is that unlikely? What is the person probably looking at?

6. Also be able to write an essay question answer for placer gold, commenting on

ü You will want to include such geomorphic features as flood plains and possibly terraces

8. In speaking of ore deposits, one often may hear reference to “gangue” minerals. What characterizes the “gangue” minerals of a deposit?

2. What is the difference between an “ore” mineral and an “industrial mineral”, according to the definitions we adopted in class?

3. Gold can be alloyed with other elements. With what other element is it most commonly alloyed in nature? And is it more often alloyed or is it more often pure Au in nature?

4. Be able to tell, for example, what is meant by the term “14 karat gold”. Similarly what is meant by, for example, gold “750 fine”.

5. Name at least one mineral in which gold occurs as a compound. Also what element is it compounded with? [Note: by “compound” here I do not mean “alloy”.]

Lecture 15, Thursday, 10/12/06

1. Is copper most often found as a compound or as native copper in nature?

2, When copper is found as a compound, with what element is it most often compounded?

3. _____When copper is found as a native element, in what kind of setting is it most commonly found?

a) In hydrothermal veins associated with plutons in a continental setting

b) In hydrothermal veins associated with plutons in a suboceanic setting

c) In volcanogenic exhalative deposits

d) In the oxidized zone of deposits that have copper in other minerals

4. _____In what kind of situation do we most often find native silver?

a) In hydrothermal veins associated with plutons in a continental setting

b) In hydrothermal veins associated with plutons in a suboceanic setting

c) In volcanogenic exhalative deposits

d) In the oxidized zone of deposits that have copper in other minerals

5. From the question above, it is obvious that I concede that silver does occur in nature as a native element. However, in nature is the element silver (Ag) most often found as native silver, or is it more often in a compound?

6. When silver does occur in a compound in nature, with what element is it most commonly compounded?

7. _____With what kind of igneous rocks are “magmatic ore” deposits of chromite and platinum associated?

a) large mafic/ultramafic intrusions

b) small mafic/ultramafic intrusions

c) large granitic (felsic) batholiths

8. Write a brief discussion of how chromium and platinum become concentrated into economically exploitable concentrations in “magmatic ore” deposits of chromite and platinum.

[Note, that whenever I ask questions like this, you should describe the geologic situation in which the elements involved are of low concentration spread out over a large volume, and then cover the geologic process that brings the elements involved to be concentrated into economically mineable deposits.]

9. What is meant by a “pegmatite” deposit? Also name at least three economically important minerals that are sometimes found in exploitable concentrations in a pegmatite.

10. Write a brief discussion of how relatively rare elements in economically important minerals get concentrated into economically exploitable concentrations in “pegmatite” deposits.

11. _____Concerning diamonds, what two rock types are associated with “diamond pipes”? (choose from below) Are these rocks considered felsic, intermediate, mafic, or ultramafic? (circle correct)

[In class I mentioned how the pressures required to grow diamonds in the lab could only be produced in the earth at depths of >150 km or so (mantle depths). However, I did not mention the coesite inclusions that have been found (although I did mention this back when we studied coesite as a high pressure polymorph of SiO₂). Also I mentioned in class, but only in passing, that in the breccia associated with kimberlite there are xenoliths commonly found of rock believed to be of mantle origin.]

13. Why do diamonds commonly have rounded off corners and edges in natural diamond occurrences?

[We pointed out how diamonds reabsorb into the magma as it rises to lower pressures. During ascent they start to resorb a little at the corners first, rounding the diamonds. Slower emplacement leads to more resorbing and hence more rounding of corners. If the kimberlite or lamproite rises too slowly all the diamond will dissolve back into the magma.]

14. What evidence is there that diamond-bearing igneous rocks were emplaced explosively?

2. ______Which element listed below is the most stable in the weathering environment (tends to be left behind in an insoluble compound in the soil, regardless of how intense the weathering is)?

4. ______I will list several pairs of minerals you may or may not be familiar with. One of the pairs has minerals that constitute bauxite. Which is it?

5. Describe in a few sentences how bauxite forms. Be sure to indicate what kinds of minerals need to be present before the bauxite-forming process begins and the kind of conditions under which bauxite forms.

6. Name two minerals of economic importance that are typically associated with “evaporite” deposits.

12. Feldspathoids are in some ways similar to feldspars. In what way is the chemistry of the feldspathoids similar to the feldspars, and in what way is the chemistry different?

13. Name two feldspathoid minerals and give the basic chemical composition of each (subscripts are not required).

14. In what kind of geologic situation are feldspathoids most commonly found? [Don’t just say igneous rocks, but you should indicate from a silica-poor and alkali-rich igneous melt.]

15. What about the structure of the zeolite minerals makes them useful as a "molecular sieve"?

16. What kind of rocks tend to host the growth of zeolite minerals, and under what kind of circumstances do zeolites form in such rocks?

[I may not have made it clear that these most commonly occur in certain volcanic rocks that have undergone very low grade metamorphism.]

17. What is the difference between "dioctahedral" and "trioctahedral" sheet silicates? Include what elements are involved and what the significance of "di" and "tri" is.

18. Describe briefly the structural differences among many sheet silicate minerals with regard to the arrangement of tetrahedral and octahedral sites (describe the significance of “tet-oct-tet” and “tet-oct” sheet silicates).

19. Characterize muscovite and biotite as to their fundamental structure (arrangement of tetrahedral and octahedral sites) and chemistry (dioctahedral or trioctahedral).

1. In what kind of geologic situation does serpentine tend to be most commonly found? (Be as specific as you can.)

2. In what kind of geologic situation does talc tend to be most commonly found? (Be as specific as you can.)

3. You are asked to assess the likelihood of asbestos occurring in a certain state in its bedrock formations. Below are listed various bedrock terranes of the state, characterized by the kinds of rocks in each terrane. Which, if any, of the terranes that make up different bedrock of that state are likely to have asbestos minerals?_____ (remember what chief mineral can occur as asbestos)

4. Tell me one property (either chemical or physical) that is similar in both talc and serpentine that is a factor in them both occurring in a similar geologic situation?

5. Besides Si, what element (cation) characterizes the chemistry of most clay minerals?

7. Is kaolinite more likely to be produced under mild weathering conditions (not too hot or humid) or under more intense weathering conditions (hot and humid)?

8. Most clay minerals have higher cation exchange capacity (CEC) than most other types of minerals. However, montmorillonite has its CEC in a way that is different than the way most other clays have it. Describe the basic difference in where the exchangeable cations are in montmorillonite as opposed to other clays.

9. Does montmorillonite have generally higher or generally lower cation exchange capacity as compared to other clays?

10. Explain the mechanism why montmorillonite only loosely holds the exchangeable cations. Explain it in terms of the basic structure and from where in the structure the forces that loosely hold the cations arise.

11. Why are clays in general good at retarding the spread of certain ionic pollutants in the subsurface, such as “heavy metals”?

12. From the list of minerals and rocks below answer what kind of mineral most readily produces montmorillonite upon weathering_____. And also what kinds of rocks tend to have an abundance of that mineral sufficient to make a montmorillonite-rich soil develop over it______.

13. From the list of minerals above, which mineral contributes the most to the production of illite during weathering?______ And does illite generally form under normal or under intense weathering conditions (very warm humid climate). Circle one.

14. Which kind of clay has a high degree of shrink and swell behavior, and why does it do so? [Don’t just say something like “it absorbs lots of water”; go ahead and explain why it does so.]

15. Where in Arkansas do we have the most amounts of this shrinking and swelling clay?

16. What kind of clay is most common in Paleozoic-aged sedimentary rocks of Arkansas (and Paleozoic sedimentary rocks elsewhere)?

18. What two clay minerals are common in “mixed layer” clays? And which one is more prevalent in older sediments and rocks?

(Note: I sent email and made some calls alerting everyone that we had to move the lecture test up to Thursday 10/26/06)

1. An aquifer is found to have arsenic in the water in concentrations determined by the EPA to be too high for safe consumption. The regulating authorities are looking for the industry that is to blame for this pollution. What might be wrong with their assumption that some industry is to blame?

2. A number of elements (such as heavy elements, arsenic, etc.) have been identified as pollutants because of toxicity to humans and other creatures. In class I listed about 4 or so, but many others could be listed. Name three minerals that can occur naturally that have elements of this nature and thus can be a source of natural pollution. Also name the element each mineral is responsible for (chemical symbol for the element is OK).

3. What kind of rock bodies (geologic setting) most commonly have minerals that can be classified as asbestos?

[In an earlier lecture I spoke of talc and serpentine forming from metamorphism of ultramafic igneous intrusions (or hydrothermal alteration of ultramafic intrusions), and of course where there is serpentine there can be crysotile asbestos. I forgot to reinforce that in class today. Also it is common for the asbestiform amphiboles we spoke of to form in similar conditions.]

5. Microscopically, what is the chief indicator that a mineral fiber is true asbestos?

8. What is the most common asbestos mineral and what is the most toxic asbestos mineral?

10. What is the basic mechanism of the cause of “acid mine drainage”? Be sure to include the role of the most common kind of minerals that are involved, and the role of the water table.

11. When an underground mine is closed, the initial ground water that comes out of the mine when it is filled with water (i.e. seeping into the surrounding bedrock aquifer) tends to have ______.

12. Explain why mine waste piles are a potential source of “acid mine drainage”.

13. If some form of toxic ionic element in a solution were released inadvertently onto the ground and began to soak into the ground, a clay-bearing soil would be ______ with regard to the potential spread of the pollutant as compared to a sandy soil devoid of clay.

14. In what way can clay minerals be involved with the spread of ionic pollutants in the surface environment?

Minerals		Rocks
a) hornblende	g) biotite	m) granite	s) sandstone
b) gypsum	h) chalcopyrite	n) shale	t) dolomite
c) calcite	i) plagioclase	o) limestone	u) gneiss
d) garnet	j) olivine	p) felsic volcanic	v) syenite
e) quartz	k) beryl	q) mafic volcanic	w) alkaline igneous rocks
f) K-feldspar	l) pyrite	r) mica schist	x) siltstone