November 2023 Polished Stones: Stone of the Day #16

Stone of the Day #16 appears to be a fine-grained mudstone, maybe argillite. It contains a variety of dark markings, either from darker sediment layers, disrupted and displaced by stresses, or from trace fossils such as tracks and burrows.

This is a larger stone than many of the previous Stones of the Day, being 7 cm by 5 cm.

I found this stone on Gemstone Beach on Friday 27 January 2023, quite early in my Southern Sojourn. Its discovery is mentioned in this Post from that time. I tumbled it in a medium 220 silicon carbide grit for about 10 days, then in a fine 400 grit and a finer 600 grit for similar periods. After nearly a couple of weeks tumbling in tin oxide polish powder, it finally had a burnishing tumble in borax for a few more days. After it had finished this tumble-polishing, I was surprised to see a scratch running across the top left-hand corner of Side A and wondered if this was caused during the tumbling. However, looking back at the photo I took of the stone when I found it on the beach, it appears the scratch was there originally. I probably did not seek to remove the scratch during the tumbling process as I wanted to preserve the dark markings.

Comparisons between the rough stone as found on the beach and the final polished stone are possible due to the photos I took then and now (though I have had to rotate Side A of the rough stone for comparisons to be made). These photos show how tumble-polishing has smoothed the stone, removing some holes, scratches and rough areas. The dark markings have sometimes changed as the surface layer was removed. First below are comparisons of Side A of the rough and polished stone. The rough stone images are on the top line of the following two sets of photos. The “Top of rough Side A” image shows the original long scratch, along with a few fingernail size indentations that were removed with tumbling (such indentations are also apparent in the “Bottom of rough Side A”):

Comparisons between the rough and polished versions of Side B again show how tumbling has smoothed out the stone but also changed some of the dark shapes (especially at lower right of image labelled “Bottom of rough Side B”, but also noticeable on the top part of the stone).

Go to Stone of the Day #17.

Go to Stone #1 in the Stone of the Day Series for November.