This image shows a simple map of the intensity of the Si X-rays produced from the polished surface of a high-grade metamorphic rock sample. Garnet and biotite, with the lowest contents of Si, are blue; potassium feldspar is green; and quartz, the richest in Si, is red. Quantitative analyses can be obtained at each point by calibration of X-ray counts (wavelength dispersive spectrometers, WDS, in this case) with known standards.
This image, from the same sample as in example 1, shows the visible light emitted from the sample as the electron beam is scanned across it. In our system, a complete optical spectrum can be collected and stored at each pixel. Here, the data are unprocessed. Fe-rich minerals garnet and biotite are black, as the Fe quenches cathodoluminescence. Several minerals appear red; perthitic potassium feldspar appears blue in this sample.
This image is from the same sample as in examples 1 and 2. Here, however, the CL color bands assigned to each screen color have been adjusted to highlight more subtle differences in the optical emissions, which can distinguish more different minerals than the unprocessed data above. Garnet and biotite are again black; potassium feldspar is purple; quartz is red; and sillimanite is green.
Backscattered electrons can be rapidly imaged to give a quick, high-resolution grey-scale picture of the sample, in which the brightness scales with the mean atomic number at each point. In this example from a fine-grained sedimentary rock, the black areas are pore spaces, medium gray is quartz, lighter grey is potassium-rich feldspar, and speckled areas are kaolinite. The scale bar is 100 microns long; features a few microns across can readily be distinguished without additional magnification.
In this X-ray image of the same rock as in example 4, X-ray counts from three elements were collected simultaneously on three wavelength-dispersive spectrometers (WDS), color-coded as shown, and combined to create a map in which minerals are clearly distinguished. Quartz (Si-rich) is blue; potassium feldspar (K+Al rich) is yellow; kaolinite (Al-rich, no K) is green. Again, void spaces (particularly important in reservoir rocks!) are black.
The powder X-ray diffraction pattern (red line) for a hard
mineral, colored greenish by inclusions of chlorite, is well-matched by the
JCPDS data base for quartz (green lines), not that of beryl (purple lines).
In this more challenging example, the sample was a small
(<100 mg), precious (oxygen-17 enriched) synthetic sodium germanate glass
containing crystalline Na4Ge9O20 (JCPDS data base pattern in purple) and
Na2Ge4O9 (purple), growing in a glassy matrix (very broad peaks).