X-Ray Diffraction (XRD)
Exploration Technique: X-Ray Diffraction (XRD)
|Exploration Technique Information|
|Exploration Group:||Lab Analysis Techniques|
|Exploration Sub Group:||Rock Lab Analysis|
|Parent Exploration Technique:||Rock Lab Analysis|
|Information Provided by Technique|
|Lithology:||Rapid and unambiguous identification of unknown minerals.|
X-ray powder diffraction is widely used in geology, environmental science, material science, and engineering to rapidly identify unknown crystalline substances (typically in less than 20 minutes). A pure, finely ground, and homogenized sample is required for determination of the bulk composition. Additional uses include detailed characterization of crystalline samples, determination of unit cell dimensions, and quantitative determination of modal amounts of minerals in a sample. X-ray powder diffraction can also be applied to the identification of fine-grained minerals. More specifically, the technique can be used to distinguish between different clays and mixed layer clays that are optically similar, but form from distinctly different weathering and hydrothermal alteration processes.
Single-crystal X-ray diffraction is used most commonly for determination of unit cell dimensions and the position of atoms within a crystal lattice. This can be applied to the identification of new minerals and to answering specific questions concerning the chemical makeup and atomic structure of crystalline substances
Single-crystal X-ray diffraction is most commonly used for identification of new minerals and for answering specific questions concerning the chemical makeup and atomic structure of crystalline substances. As such, the application of this technique in modern geothermal exploration is fairly limited.
- Rock Lab Analysis
In X-ray diffraction, a device called a goniometer is used to rotate the sample in the path of the incident beam at an angle Θ, while an arm-mounted X-ray detector is maintained at an angle of 2Θ (typically from about 5-70° for a powdered sample). For X-ray powder diffraction, a single goniometer is used orient the sample and detector. In single-crystal X-ray diffraction, between 3- and 4-circle goniometers are used, each referring to one of four angles (2Θ, χ, φ, and Ω) that define the relationship between the crystal lattice, the incident ray, and the X-ray detector.
Analysis of clays requires that the sample have a single orientation. This type of analysis requires specialized sample preparation techniques, which are outlined in detail on the USGS website.
Additional limitations of XRD analysis include:
- Unknown mineral identification is best accomplished using a homogeneous and single phase sample.
- Interpretation of the data requires access to a standard reference file of inorganic compounds.
- Requires a relatively small amount (tenths of a gram) of pure material that has been ground into a powder.
- The detection limit is about 2% of the sample for mixed materials.
- Indexing of patterns for non-isometric crystal systems can be complex for unit cell determinations.
- Peak overlay may occur for some samples and becomes worse for high angle “reflections.”
- For single-crystal analysis, a single, stable, optically clear crystal sample is required, generally between 50 to 250 microns in size. Twinned samples can also be analyzed, but with greater difficulty.
- Data collection times for single-crystal analysis are significantly longer, usually between 24 and 72 hours.
Campana, C.F., Bruker Analytical Application Note
Cullity, B. D. 1978. Elements of X-ray diffraction. 2nd ed. Addison-Wesley, Reading, Mass.
Eby, G.N., 2004, Principles of Environmental Geochemistry. Brooks/Cole-Thomson Learning, p. 212-214.
Klug, H. P., and L. E. Alexander. 1974. X-ray diffraction procedures for polycrystalline and amorphous materials. 2nd ed. Wiley, New York.
Moore, D. M. and R. C. Reynolds, Jr. 1997. X-Ray diffraction and the identification and analysis of clay minerals. 2nd Ed. Oxford University Press, New York.
Putnis, A. (1992). Introduction to Mineral Sciences. Cambridge, UK: Cambridge University Press. Chapter 3 (pp. 41-80).
- X-ray Powder Diffraction (XRD)
- Single-crystal X-ray Diffraction
- Michael L. Sorey,Gene A. Suemnicht,Neil C. Sturchio,Gregg A. Nordquist. 12/1991. New Evidence On The Hydrothermal System In Long Valley Caldera, California, From Wells, Fluid Sampling, Electrical Geophysics, And Age Determinations Of Hot-Spring Deposits. Journal of Volcanology and Geothermal Research. 48(3-4):229-263.
<ref>tag; no text was provided for refs named
Cite error: Invalid
- X-Ray Reflection in Accordance with Bragg’s Law
|Page||Area||Activity Start Date||Activity End Date||Reference Material|
|X-Ray Diffraction (XRD) At Long Valley Caldera Geothermal Area (Flexser, 1991)||Long Valley Caldera Geothermal Area||1985||1988|