2018年10月23日記事で、球がくっつきあったような、バイカル湖底に転がる不思議な石を紹介しました。地質調査所の知り合いも見たことがないというので、ノボシビルスクにある地学研究所にいるロシア人の友人に成因などを調べてもらったところ、下記の回答が来ました。生物の作用による堆積岩との結論に至ったようです。ただ、海綿が生息する水域はバイカル湖だけではなく、他の水域でこんな石が見つかっていないので、納得できない気持ちが半分です。
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After consultations with specialists we decided that this stone is trivial coarse-grained sandstone (with particles of gravel). It means that this is an ancient sedimentary rock. Why its surface is so spherically carved, I don't have a conclusion. Prof. Shcherbakov Dmitry Yurievich, who brought this stone to me, told that it is from sponges and they often drag such stones from the depth of the Baikal. However he did not explain in detail the structure and origin of such stones. From my point of view, such surficial structure should be biogenic. I read that specific sponges, which form crusts on stones, digests by chemical elements from the stones. They produce acids, which dissolve the surface and release chemical substances. This process obviously should be more active near edges of the sponge bodies. This may be the reason of the spheric units.
