False-colour scanning electron micrograph of anhydrous caffeine crystals (1,3,7- trimethylxanthine). They were produced by sublimation, that is, by heating the solid until it is vapourised, then condensing the vapour. This drives water out of the structure resulting in anhydrous crystals. Examples of twinning can be seen here, where crystals at different orientations interpenetrate producing cross shapes. Caffeine stimulates the central nervous system. It is often contained in analgesic preparations with aspirin or codeine, and it is a diuretic. It occurs in coffee beans, tea leaves & cola nuts. Magnification: x240 at 6x4.5cm size.
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