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A new procedure for relocating mineral grains for microprobe analysis

Published online by Cambridge University Press:  05 July 2018

P. J. Potts ,
A. G. Tindle  and
D. Stanford
P. J. Potts
Affiliation:
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
A. G. Tindle
Affiliation:
Department of Earth Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
D. Stanford
Affiliation:
Department of Biology, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
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Abstract

A new procedure is described for locating mineral grains in geological samples prepared for microprobe analysis. This procedure uses a digital image of the entire sample surface to select points of interest. These features of interest must be visible in this external image. Once the sample is mounted on the specimen stage of the microprobe, the digital image is used as a ‘map’ to relocate minerals for analysis. The image can be recorded using either a video camera, fitted with a macro zoom lens, or a flat-bed scanner. A calibration procedure has been developed in which two indexing points are used to calculate the instrument stage coordinates from the pixel coordinates of the digital image. Following this calibration, the stage coordinates of any feature visible in the digital image can be displayed to facilitate rapid relocation. The procedure was evaluated by relocating magnetite grains visible in an optical image of a geological thin section. The repositioning accuracy in relocating 28 magnetite grains distributed over an area of about 20 × 30 mm was found to be 157 ± 102 µm (one standard deviation) from the video camera image and 48 ± 28 µm from a flat bed scanner image. The former image was thought to suffer from some optical distortion. The procedure may be applied to any microprobe instrument fitted with a digital x-y specimen stage. Future applications in relocating features visible in autoradiographs are currently being evaluated.

Keywords

microprobe analysismineral grainsgrain location
Type
Image analysis
Information
Mineralogical Magazine , Volume 59 , Issue 395 , June 1995 , pp. 221 - 228
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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