Page 16 - Curriculum Visions Dynamic Book

Calcium carbonate
Because calcium bicarbonate is far less stable in hot water than in cold, just like the limescale on a kettle, calcium carbonate (travertine) is often precipitated around many hot springs.
The water in hot springs may have begun as pure rainwater; but by the time it has circulated through underground passages, it has dissolved much of the rock through which it is passing and thus has picked up considerable amounts
of calcium compounds in solution. As this hot water reaches the ground, it cools and the calcium carbonate is precipitated as sheets of white calcite crystals that sparkle in the sunshine.
Waterfalls that sparkle
In the most spectacular locations, such as Pammukale in Turkey and Mammoth Hot Springs in Wyoming (shown here), calcite makes beautiful stepped pools of travertine.
The streaks of other colours in the travertine are formed by other minerals or mud. The pools are enclosed by rimstone dams. These are formed as the water flows over the rim where it is more likely to evaporate. This leads to a buildup of carbonate precipitate, which increases the height of the dam wall.
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 Calcium sinter