Thin section
A thin section is a slice of rock ground so thin, about 0.03 millimetres, that light can shine through it under a microscope.
Most rocks look opaque, but almost all their minerals become transparent when cut thin enough. To make a thin section, a technician cuts a small chip of rock, glues it to a glass slide and grinds it down to a standard thickness of 30 micrometres, about a third of the width of a human hair. A polished thin section, without a cover glass, can also be analysed with an electron microprobe.
Thin sections are the starting point for classifying almost every meteorite. Under a polarising microscope, each mineral shows characteristic colours and behaviour, so scientists can identify olivine, pyroxene, plagioclase and glass, judge how sharp the chondrules are, estimate the petrologic type and assign a shock stage. Opaque minerals, such as iron-nickel metal and troilite, are studied with reflected light instead.
Thin sections of the Allende CV3 chondrite are popular teaching specimens, showing chondrules, CAIs and dark matrix side by side. A finished section looks like a pale, glassy film on a microscope slide. Making one needs diamond saws, abrasives and specialist skills, so this is laboratory work and not a home project.
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