Scanning electron microscope
An instrument that scans a finely focused beam of electrons across a sample to build highly magnified images and chemical maps.
A scanning electron microscope (SEM) sweeps a beam of electrons, focused to a spot far smaller than a light microscope can resolve, across a polished section or a rough fragment. Detectors collect the signals that come back. Secondary electrons record surface relief, while backscattered electrons (BSE) give contrast by mean atomic number, so iron-nickel metal and sulfides glow bright, olivine and pyroxene appear mid-grey and feldspar and glass look darker.
Most SEMs also carry an energy-dispersive X-ray spectrometer (EDS), which identifies elements from the characteristic X-rays each one emits. That lets a researcher map where calcium, aluminium or sulfur sit within a chondrule, locate tiny phases worth analysing with an electron microprobe, and spot presolar grains or alteration minerals only micrometres across. Classification of new meteorites, especially in recognising textures and shock melt, leans heavily on BSE mosaics.
A familiar example is the CV chondrite Allende: BSE images of its calcium-aluminium-rich inclusions reveal concentric mineral rims and intricate intergrowths invisible by eye. You will recognise SEM work by its greyscale images with a micrometre scale bar, and by false-colour element maps in which each colour stands for a different element.
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Level: Expert Advanced