December 18, 2001 name: ___________________GS 231: Mineralogy Final Exam1. (20 points) Island Silicatesa. Give the formulae and names of the common Mg and Fe2+ end-member species of olivines andgarnets in the table below.element olivine formula garnet formulaMgFe2+b. Given the binary melting diagram for the Fe - Mg olivines, what can be concluded about the degree ofsolid solution and why?c. An unusual olivine, monticellite, is known with a formula involving one mole of Ca and one mole ofMg. Given other mineral systems with similar chemistry, is it likely that monticellite may be found withMg olivine or not? Give a brief explanation of your conclusiond. A surprising find is the occurrence of a fully oxidized olivine called laihunite. Without knowing aboutlaihunite, which has been found rarely in altered and oxidized iron formations metamorphosed at high P-T, provide a possible mechanism by which ferric iron may substitute in olivine.2. (20 points) Chain Silicatesa. (5 pts) List the different types of chain silicates based on fundamental differences in their basicstructures.b. (5 pts) The chemical classification of the main pyroxene and amphibole groups is similar. Withoutlisting individual mineral names and formulae, Give four major chemical series that apply to both groups.c. (10 pts) Sketch the pyroxene quadrilateral in its standard form and label the corners. What pyroxeneseries lie within the quadrilateral rather than along or very close to the edges? Show the areas withexpected solid solutions with light shading and indicate where solvi are found with tie lines between thecoexisting pyroxenes.3. (15 points) Sheet SilicatesThe common sheet silicates may be distinguished by their basal spacings and whether they aredioctahedral or trioctahedral.a. Fill in the table below with the names of the common Mg-rich and Al-rich sheet silicates. If nocommon representative is known, put a dash in that section of the table. For each group indicate thenature of the tetrahedral and octahedral layers in shorthand (i.e., TO structure).basal dioctahedral trioctahedral T&O bondsspacing7 Å _____________________ _____________________ _____________9.3 Å _____________________ _____________________ _____________10 Å _____________________ _____________________ _____________14 Å _____________________ _____________________ _____________b. Chlorite is a hydrated magnesium aluminum silicate. What mineral assemblage might it react to formin the absence of quartz?c. Pyrophyllite is a hydrated aluminum silicate. What mineral assemblage involving one or more indexminerals might it react to form? Balance the exact reaction(s).4. (20 points) GeochronometersThe minerals zircon, monazite, and xenotime are common accessory minerals in a wide variety ofcrustal settings, ranging from concentrates in sand deposits, to metapelitic and granitic rocks.a. Give the formulae for zircon, monazite and xenotime.b. Which two of these minerals is isostructural and which one is not? What might that predict for mutualsolid solutions between these phases?c. What are the most common solid solutions in zircon, monazite and xenotime?d. Why do these minerals occur in only sparse amounts in most occurrences?e. How are these minerals used to solve important geological problems as geochronometers?6. (25 points) Evaporite Mineralsa. (10 pts) Given the chemistry of sea water, what are the most common minerals that form in evaporitedeposits? List one mineral that contains each of the listed constituents of sea water as one of its majorconstituents, and give its formula. The same mineral may be used more than once.element chemistry mineral formula solubility order of crystallizationCl-19.0 wt %Na+10.5 wt %SO42-2.7 wt %Mg2+1.2 wt %Ca2+0.4 wt %K+0.4 wt %HCO3-0.1 wt %total salts 34.4 wt %b. (5 pts) Which of these minerals is the most soluble in water and which is the least soluble? Numberthe phases you listed in the table above in order of their increasing solubility in water.c. (5 pts) Number each of the minerals in the table above in terms of their sequence of crystallization interms of continuously evaporating an aliquot of sea water in the table above.d. (5 pts) Briefly explain below why this simple evaporation model seldom if ever applies to sedimentaryevaporite deposits that are produced in