Lamprophyre Dyke at Moulin Huet 9 – Strange natural honeycomb textures in the weathering surface of a lamprophyre dyke (right of image) cutting through Icart Gneiss (left of image) at Moulin Huet Bay in the Southern Metamorphic Complex on the Channel Island of Guernsey.
Jessica's Nature Blog 
To a real novice the circular depressions in the rock appear to be caused by gas bubbles in the molten rock.
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Perhaps you are right. They do look like gas bubbles. I will keep looking for information. Much has been written on the composition of such dykes but it is not always easy to understand because of the specialist terminology used.
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