Salt and peppercorn. Coloured scanning electron micrograph (SEM) of a salt grain (blue) and a peppercorn (brown). Salt (sodium chloride) is a crystalline compound. It is commonly obtained from salt mines or by the evaporation of sea water, and used to flavour and preserve food. The peppercorn is the fruit of the tropical vine Piper nigrum. Ground peppercorns are used as a hot aromatic food seasoning. Magnification: x6 at 6x7cm size.