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Calthemite. Or cave forms in bunkers.

Olli and I went to Sepänkylä to visit more bunkers, and to fly our drones. We found a standard Soviet Porkkala bunker model, relatively intact except for the room under the gun hole. But what wonderful flowstone!

I've also been doing some reading about stalactites and concrete. Stalactites and flowstone are examples of speleothems; in concrete structures such as bunkers, these can grow very quickly. But they are technically not classified as speleothems in concrete, because the definition of the relates to caves:

    Definition 1. Speleothems are secondary mineral deposits formed in a cave [ 1].

Flowstone is sheetlike deposits of calcite or other carbonate minerals [ 2], in a cave environment. In concrete, it is called concrete derived flowstone [3]. This is an example of calthemite:

    Definition 2. Calthemite is a secondary deposit, derived from concrete, lime, mortar or other calcareous material outside the cave environment [ 4].

What I definitely did not know before was that calthemite and speleothems actually form with different chemical reactions. Calthemite comes from calsium hydroxide (leftover from making concrete) reacting with carbon dioxide as the two come into contact when dripping water from the concrete reaches air:

    Reaction 1: Ca(OH)
    2

    (aq)
     + CO
    2

    (g)
     → CaCO
    3

    (s)
     + H
    2
    O
    (l)   
    [3]

The resulting solution contains calcium carbonate, some of which will be left on the surface as the water drops away.

But regular cave speleothems form through calcium bicarbonate (from dissolving limestone) reaching air and turning to calcium carbonate:

    Reaction 2: Ca(HCO
    3
    )(aq)
    2
     → CaCO(s)
    3
     + H
    2
    O
    (l)
     + CO(aq)
    2
      [5]

In other words, both processes end up with calcium carbonate on the surface of the growing flowstone or other speleothem/calthemite, but the process at which they come to this is different.

While cave stalactites grow very slowly, few millimetres per year, calthemite can grow much quicker. A calthemite straw stalactite can grow 2 millimetres per day in optimal environments [3].

Here are more pictures of the flowstone. I mean concrete derived flowstone:

Forest and the bunker from above:

The entrance and emergency exit:

And here's the drone pilot:

Tämä blogi löytyy myös suomeksi Relaasta. This blog is also available at the Blogspot site. Photos and videos (c) 2018 by Jari Arkko and Olli Arkko. All rights reserved. The song "Hollywood High" is by Silent Partner, and freely available from YouTube audio library.

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