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2 Exam 2003 - This question paper consists of I...

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Unformatted text preview: This question paper consists of I pr-r‘nrea’page identified by the code number E'AR5'202201 EARS 202201 © UNIVERSITY OF LEEDS School of Earth Sciences May/June 2003 Examination for the degree ofBachelor of'Science Environmental Mineralogy Time allowed." 2 hours Answer FOUR questions, TWO from Section A and TWO from Section B SECTION A - Answer 2 questions (25% each) 1. All silicate minerals can be subdivided into four main groups based on their composition and structure. Outline the structure, chemical composition and diagnostic features of TWO of the groups listed below; illustrate your answer with at least TWO different mineral phases from the group selected: a) orthosilicate group; 13) chain silicate group; c) sheet silicate group; d) framework silicate group. 2. With the aid of simple P—I, G—T and G—P plots, describe how Gibbs Free Energy (G) can be used to determine which phases are stable under particular conditions (eg. P and/or I). 3. Give two examples of minerals that exhibit ideal (continuous) solid—solution For each example, state the end-member compositions and the cations that substitute for each other F or both examples draw their T-X phase diagrams with properly labelled curves and stability fields. SECTION B — Answer 2 questions (25% each) 4. (a) What is the sequence of mineral deposition and what changes are observed in fluid chemistry during the evaporation of a marine brine? (b) Which group of minerals is indicative of continental (playa lake) evaporites. Why are these minerals not found in marine evaporites? 5. (21) Compare the structure and general mineral chemistry of kaolinite with that of montmorillonite (smectite). (b) How do these differences influence the respective cation exchange capacities (CEC) ot'the two minerals? 6 (a) What is meant by the term extra-framework cation? (b) Which cations are the dominant extra-framework cations in zeolites? (0) Discuss the factors that influence the growth of zeolites in sediments. {:NJD ...
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