Complete Lab 7 all through Excel. No written work is needed. Provide a workbook with the answers and solutions.
GEOL 3370 MINERALOGY Lab 7 Crystal Chemistry Name:___________________________ Lab Time:_______________________ Mineral Calculations (show all steps in the calculations) Example 1: To calculate the composition, in terms of weight percent oxides, of the mineral wollastonite, CaSiO3. Wollastonite is CaSiO3. The molecular weight of CaO is 40.08+15.9994 (AW Ca + AW O) = 56.0794 The molecular weight of SiO2 is 28.0855+(2 x 15.9994) = 60.0843 The molecular weight of CaSiO3 is 56.0794 + 60.0843 = 116.1637 The percentage by weight of CaO in CaSiO3 is (56.0794/116.1637)*100 = 48.28 The percentage by weight of SiO2 in CaSiO3 is (60.0843/116.1637)*100 = 51.72 Chemical composition of wollastonite CaO 48.28 in weight percent oxides SiO2 51.72 Total 100 Alternative method Wollastonite is CaSiO3 The atomic weight of Ca is 40.08. The atomic weight of Si is 28.055. The atomic weight of O is 15.9994. The molecular weight of CaSiO3 is 40.08+28.0855+(3 x 15.9994) = 116.1637 The percentage by weight of Ca in CaSiO3 is (40.08/116.1637) x 100 = 34.50 The percentage by weight of CaO = 34.50 x 1.3392 (oxide factor) = 48.27 The percentage by weight of Si in CaSiO3 is (28.0855/116.1637) x 100 = 24.17 The percentage by weight of SiO2 = 24.17 x 2.1393(oxide factor) = 51.71 Chemical composition of wollastonite CaO 48.27 in weight percent oxides SiO2 51.71 Note the slight difference that arises because of rounding errors. You should carry all these calculations to 4 places of decimals to minimize such errors. Example 2: To calculate the chemical formula of a mineral with the composition CaO=41.24 wt %, TiO2=58.76 wt%. Divide by oxygen factor wt% element Divide by AW atomic prop CaO 41.24 41.24/1.3992 =29.47 29.47/40.08 =0.7353 Ca TiO2 58.76 58.76/1.6680 =35.23 35.23/47.90 =0.7354 Ti _____ ______ 100.0 64.70 Difference 100 – 64.70 = 35.30 wt% oxygen 35.30/15.9994 =2.2063 O Atomic proportions are Ca .7353, Ti .7354, O 2.2063 Normalize to 24 oxygens, Ca = .7353 * (24/2.2063) = 7.9985 Ti = .7354 * (24/2.2063) = 7.9996 O = 2.2063 * (24/2.2063) = 24 Formula is Ca7.9985Ti7.9996O24 or better CaTiO3 1. Calculate the chemical composition of: a) ilmenite FeTiO3 b) cordierite (Mg,Fe)2Al4Si5O18 (assume equal numbers of Mg and Fe atoms; so make up a mineral formula for a cordierite with equal Mg and Fe) c) labradorite An50Ab50 (equal amounts of albite and anorthite; make up a mineral formula for a plagioclase with equal albite and anorthite) Assume stoichiometry. Express the final analysis in terms of weight percent oxides, i.e., SiO 2 = x.xx weight percent, etc. 2. The mineral pyrrhotite has the formula Fe(1-x)S. Calculate the value of x for each of the following analyses: Element 1 2 3 Fe 56.49 61.49 56.74 Co 1.50 0.49 Ni 4.30 0.39 1.10 S 36.71 37.18 41.67 insol. resid. 0.33 0.46 ____ ____ ____ 99.33 99.52 100.00 Ignore the insoluble residue; include atomic Ni and Co along with Fe, i.e., in the same atomic site. 3. Given the following analytical data, calculate the chemical formula for the two minerals and hence identify the minerals. Values given are in weight percent. a) Cu = 63.3, Fe = 11.1, S = 25.6 b) SiO2=38.0, Al2O3=21.5, FeO=26.6, MgO=6.3, MnO=7.6 Calculate b) in terms of a formula with 12 oxygens. 4. A rock is made up of 17% quartz, 38% magnetite, and 45% ilmenite by weight. Calculate the chemical composition of the rock. The answer should be in the form of a chemical analysis with all the components given as weight percent oxides. Procedure: Determine the weight percent SiO2, from the amount of quartz (SiO2); there is no other SiO2 From the amount of magnetite, determine the amount of FeO in magnetite and Fe2O3 in magnetite (magnetite is Fe3O4; there is one FeO for each Fe2O3 in molecular amounts, not by weight). From the amount of ilmenite, determine the amount of FeO in ilmenite (ilmenite is FeTiO3; for each FeO there is one TiO2 in molecular amounts, not by weight), and also the amount of TiO2 in ilmenite. Combine the FeO in magnetite and ilmenite. List the weight percentages of the various oxides (SiO2, TiO2, Fe2O3, FeO) 5. You are given the relative amounts of these three minerals by weight (in Question 4). Calculate the volume percentages of these minerals in the rock. Answer on a separate sheet(s) of paper. Your answer should be neat, arithmetically correct, and should show each step in the calculation. GEOL 3370 MINERALOGY Lab 7 Crystal Chemistry Alternative method