False-colour scanning electron micrograph (SEM) of fur from a domestic kettle, showing the crystals that form in a hard water area. Kettle fur consists of needles of calcium sulphate which precipitates out of hard water into regular crystallographic shapes. The geologist knows calcium sulphate as anhydrite. Its monoclinic crystallographic lattice & flower-like clumps of needles are also the most common form in nature & it is from rocks bearing anhydrite that water derives its hardness. When water containing calcium sulphate is boiled or evaporates, the calcium sulphate precipitates out of solution. Magnification: x115 at 35mm. Gold tint. Original is BW A600/300. Reference: MICROCOSMOS, figure 7.17, page 135.
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