About Equipment
X-ray Powder Diffraction
For X-ray Powder diffraction, the RRUFF™ project uses the Bruker D8 Advance. A powdered sample is examined from 5° to 90° 2-theta at 2.0 seconds per 0.010° step using Cu radiation. The data is matched against the ICDD, and the unit cell is refined using (h k l) values from the American Mineralogist Crystal Structure Database.
Single Crystal CCD Diffractometer
Crystal orientations are determined using a Bruker Apex X8 single crystal diffractometer. Analysis of diffraction spots from the X8 produces 3x3 matrices that describe the orientation of each crystal. The crystal can then be fixed on a pin in a chosen orientation for use with oriented experiments. The pin is specially designed with a flat edge in order to unambiguously define two perpendicular crystallographic directions. In certain cases, powder diffraction is not feasible. Single crystal technique can be used to identify single grains as small as 25 μm in diameter.
Raman Spectroscopy
Several Raman spectrometers are used for the RRUFF™ Project. The Downs group has both a custom-designed unit with a 514 nm laser and a commercial Thermo Almega XR with 532 and 780 nm lasers. To obtain spectra from oriented samples we built a high-precision translation and rotation stage and goniometer for the optical bench.
Denton’s group has a 785 nm system that was the prototype of the Thermo instrument. Rossman’s lab at Caltech has a Kaiser Optical Systems HoloProbe 785 and a Renshaw microRaman system for work at 514.5 and 780 nm.
Electron Microprobe
Electron Microprobe Analysis is used to determine the chemical composition of the minerals. We use the UA's modified CAMECA SX50. The operator selects twenty points in the smoothest area of a polished sample for qualitative and quantitative WDS analysis. Analysis of the experimentally determined elemental compositions provide the chemical formula.
