Geol 2311 12/11/06 Lab 20 – X-ray Powder Diffraction Analyses Due Date: Tues, December 19. Total Points 15 Objective: Become familiar with X-ray powder diffraction analytical methods and attempt to identify unknown mineral samples collected from the field trip. Procedure: Work in groups of 3-4 to prepare and analyze a mineral sample from the field trip. The XRD analysis and peak matching will take about 60 minutes, but sign up for a 2-hour time slot (sign-up sheet is on lab door) some time between Tuesday and Thursday afternoon. Be sure that the person putting the sample in the XRD wears the dosimeter ring. After conducting your analysis, turn in a group report which includes the following information: 1) sample location 2) sample description (describe physical attributes of your sample and what part of sample you are planning to analyze) 3) sample preparation (describe how you extracted the mineral sample) 4) speculation of possible minerals in your sample. 5) 2θ diffraction peak plots of the quartz standard and your unknown sample with possible mineral matches. Briefly state how confident you are of the minerals you have IDed. Sample Preparation: Extract the mineral(s) you wish to analyze from the host rock. If it is coarse, crush it in the shatter piston apparatus. Grind the fine mineral sample in an agate mortar and pestle to a very fine powder. Pack the powder into an aluminum sample holder leaving a smooth upper surface to the sample. Starting up the XRD: 1) Turn on the water pump (behind the XRD) and the air conditioner 2) Make sure chamber doors are tightly shut. 3) Turn on the XRD power (left button on panel). Voltage and amperage will increase to 15 kV and 5mA, respectively. X-ray generator and detector arms will move into position resting at 2θ = 5°. 4) Enter name and start time in log book. 5) Boot up the computer. Silica standard analysis: 1) Open the sample chamber doors and insert the silica standard into the sample holder. 2) Close the doors tightly 3) On computer desktop, double click on Phillips X’pert Organiser icon; enter “class” as user name and password. 4) From the upper menu, pull down “Users and Projects” and select “select projects” 5) Select “Mineralogy” project 6) From the upper menu, pull down “Modules” and select “Xpert data collector” 7) From data collector upper menu, pull down “File” and select “open program” 8) From the list, select “QTZ STD 10-30 1min” scan (this is preset program to quickly scan 2θ from 10-30°). 9) Close this window (x box in upper right) 10) From the upper menu, select “Control” and click OK, then OK again to message 11) Hit “Change kV/Ma” button12) Increase Tension to 40kV and Current to 45mA; click OK. 13) Minimize this Control window 14) From the upper menu, pull down “Measure” and select “program” 15) Select “QTZ STD 10-30 1min”; click OK 16) Give run name w/ group name (e.g., Qtz std Group Leica); click OK 17) Analysis will take about 60 seconds and will plot X-ray intensity vs. 2θ from 10-30°. 18) When analysis is completed, maximize the Control Window 19) Decrease the Tension to 30kV and the Current to 10mA; click apply Unknown Sample Analysis: 1) Open the sample chamber doors; remove the silica std; insert the unknown sample holder 2) Close the sample chamber doors tightly. 3) Increase Tension to 40kV and the Current to 45mA; click Apply; minimize window 4) From the upper menu, pull down “Measure” and select “program” 5) Select “CLASS 5-65”; click OK 6) Give run name w/ group name (e.g., Amygdule sample Group Leica); click OK 7) Analysis will take about 30 minutes and will plot X-ray intensity vs. 2θ from 5-65°. 8) Be sure at least one person in present during the analysis; you may evaluate the quart standard while you are waiting (see below). 9) When analysis is complete, maximize the Control Window 10) Decrease the Tension to 30kV and the Current to 10mA; click apply Evaluating the Quartz Std and Unknown Mineral Peaks: 1) Minimize the Organizer window to return to the desktop 2) Click on the Phillips X’pert Graphics icon on the desktop 3) From the upper menu, pull down “File” and select “new graph” 4) Select graph you wish to peak search, click OK 5) From the upper menu, pull down “Analyze” and select “peak search”(or click peak search icon), click OK 6) Program will identify the 2θ of the various peaks with green lines. For the Quartz std, two main peaks are present and should be at 26.651 and 20.850; your peaks should be within 0.1 of this (If they aren’t, the diffractometer is out of alignment and will have to be adjusted). Click OK. 7) From the upper menu, pull down “Analyse” and select “Search-Match”(or click peak search-match icon), click OK 8) A list of minerals will appear on in a lower table of possible minerals that have matches the 2θ and relative intensities of the various peaks. Most of the minerals on this list are obscure minerals that are not likely to be in your sample. Moreover, some minerals that you might expect to be present, may not be on the list. If you want to add a mineral to the list …. 8A) click the “Insert” box. Look up the file number in the green mineral powder diffraction file book. Enter this number in the reference code box. 9) Clicking on a mineral name will show its peak positions with heavy black lines. If you think this mineral is a good fit, click on the “A” box to continuously show the peaks for that mineral in color. Some Special Tools: Change line colors – select new color from the drop down menu next to color Sort selected minerals - you may move all selected minerals to the top of the list by clicking the “sort” box and click the “Accepted patterns at the top…” box, then OK. Zooming in and out – left click a box on the area you want to zoom into. To zoom out to full screen, right click and select full view from the menu10) After a mineral has been selected, click the check box that says “Correct position of plotted peaks for specimen displacement” in the lower left of the table to adjust to the maximize the fit of the peaks. CAUTION: If the lower table happens to disappear, which can happen if you hit enter instead of OK, you can recover it from the upper menu - pull down