I had occasionally seen partly blackened cockle shells on the beach at Lower Largo, then last week I picked up two black oyster shells and a black scallop shell. I originally thought that the cause might be connected with the Fife coal deposits, but now I don't think that is the cause and I am indebted to 'Jessica's Nature Blog' for an explanation. It's quite a complicated process but as I understand it, once the animal dies the shell over time may become buried deep in the sand by the action of wind and wave power. At this deep level there is a lack of oxygen and the only bacteria that can survive are anaerobes. As these anaerobic bacteria feed on organic matter that is present in the sand they produce hydrogen sulphide. This chemical reacts with iron oxide present on the sand grains to produce iron sulphide which is black in colour and it is this which can turn the deeply buried shells black.
1 comment:
Interesting.
Post a Comment