Minerals from water

From GeoClasses

As we saw when we talked about the silicates, the stability of the minerals at the surface depends on the temperature at which the mineral pricipated from the magma. If the mineral precipitated at a high temperature it is less stable at the surface of the Earth that one that precipitated at a lower temperature. Olivine is less stable than quartz or orthoclase.

Dissolution

Limestone tombstone with lettering dissolved by precipitation

Close view of lettering on imestone tombstone with lettering dissolved by precipitation

Minerals that are less stable break down more quickly under conditions at the surface. For example, water flowing through an igneous rock (rock formed from solidified magma) is more likely to dissolve olivine crystals than quartz crystals. When minerals get dissolved the mineral breaks apart into ions.

An olivine crystal, for example, if it had the original composition MgFeSiO₄ would break into ions of Mg⁺², Fe⁺², and SiO₄⁺⁴ when dissolved in water.

Re-precipitation

Stalactite

Quartz veins

The water flowing through a newly solidified igneous rock is likely to be pretty hot, simply from the original heat of the magma. As the water moves away from the igneous pluton it cools down. Hot water can hold more minerals (ions) dissolved in it than cold water. So when the hot water with lots of dissolved minerals cools down it has to release some of the dissolved material. These dissolved ions re-precipitate to form new minerals.

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