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How does an electron microprobe measure a mineral’s chemical composition?
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geology
A rock formation called “faux amphibolite,” from the Nuvvuagittuq greenstone belt in northern Quebec, dated to 4.28 billion years ago.
An electron microprobe measures a mineral's chemical composition by focusing a high-energy beam of electrons onto a specific, highly polished, and carbon-coated thin section of rock.12
The process functions through the following steps:
- Excitation: The focused electron beam, which can be narrowed to a diameter of approximately one micrometre, strikes a single mineral grain. This interaction causes the atoms within the mineral to emit diagnostic [X-rays].123
- Measurement: The intensity and concentration of these emitted X-rays are measured by a computer. Because each element produces characteristic X-rays, this data allows for the identification and quantification of the elements present in the sample.13
- Analysis: This technique enables researchers to perform in situ quantitative analysis on extremely small mineral grains. Beyond simple spot analysis, the probe can be scanned across a mineral to detect chemical zoning or to determine the distribution of elements across the boundaries of coexisting minerals.21
This method is highly valued in mineralogy for its ability to provide precise chemical data at a microscopic scale.31