Apologies for the quality of these pictures taken way back in 2009 with my first digital camera. I just came across the images as I was sorting my photo collection. I took them on a holiday to Rethymnon on the island of Crete in the Mediterranean. At the time, I thought the strange patterns in the stone walls of the old Venetian fortress were part of the rocks themselves. Locally the bedrock is described as crystalline limestone. Looking at the pattern and texture now, I am not so certain. It looks more like something that has been caused by the weathering process. I am thinking that maybe over the centuries since the construction of the wall, the limestone has dissolved in rain water and the calcium has recrystallized in this way between the large and small rocks that make up the wall. This has in a way reinforced the wall by further binding the elements together. I don’t know whether the walls were originally built as dry stone or whether they incorporated mortar. The crystal formation seems to be acting as a mortar now.
I have seen something similar to this phenomenon on my beloved Rhossili Beach on the Gower Peninsula in South Wales. I will fish out some photos for comparison.