Scanning electron micrograph of fur from a domestic kettle, showing the crystals that form in a hard water area (Norwich, Norfolk). The fur consists of crystals of calcium carbonate (pebbles, not seen here) and crystals of calcium sulphate (needles). Hardness is caused by calcium salts; calcium bicarbonate (temporary) and calcium sulphate (permanent). When water containing calcium bicarbonate is boiled, the soluble bicarbonate breaks down to give the insoluble calcium carbonate. When water containing calcium sulphate is evaporated, boiled or dries out, the calcium sulphate precipitates out of solution. Mag:X1300 at 10x8 inch, x370 at 6x7cm size.
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