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Balls and Spheres etc

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  • Balls and Spheres etc

    CAVE PEARLS

    Cave pearls are often so perfectly round and polished that it’s difficult to believe that they aren’t artefacts.

    They’re type of “speleothem” – a concretion of calcium-based minerals typically found in caves or mines and formed when water rich in these minerals begins to deposit around a tiny nucleus such as a grain of sand. Microbial action may also play a part in triggering the formation.

    They’re found where water has been percolating from above through limestone or other carbonate-rich rocks or from natural springs rich in calcium salts and formed primarily as calcite depositions with traces of other minerals.

    More usually the dripping water carries a bit of other sediment with it and the concretions are dirty/gritty and only approximately spherical. In special circumstances such as when there is continually flowing or dripping water and the nucleus is trapped in a pool, the current or turbulence prevents it from settling to the bottom. The minerals then deposit evenly on all surfaces to create a perfect sphere which may be water polished to a high sheen. In a sense, they are spherical stalactites. Like these:


    [picture by painshill]

    They may be found singly or in multiples and are usually smaller than 1cm but may range up to about 15cm at their largest. Once they reach a certain size, become crowded in their pool or if the water flow reduces or stops (eg as a result of seasonal rainfall fluctuations), the current can no longer keep them apart or prevent them from settling to the bottom. They may then aggregate into clusters that look like bunches of grapes, concrete together and continue growing in a less even manner. They often then occur in what look like “nests” of conjoined eggs.


    [A nest of cave pearls in the Rookery portion of Lower Cave in Carlsbad Caverns, New Mexico – CC BY-SA 3.0 - Licensed under the GFDL by the author and released under the GNU Free Documentation License]

    Sometimes they will degrade and fall apart when they dry out.
    Last edited by painshill; 01-28-2016, 09:45 AM.
    I keep six honest serving-men (they taught me all I knew); Their names are What and Why and When and How and Where and Who.
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