What would this be?

You should place something with a scale next to it. A ruler, a quarter, a banana... something to give an idea of size.

I've seen stuff like that before on the beaches of Crete, along with lots of bits of pottery. Can't help I'm afraid, but it's probably some sort of packing, or transportation object. The Roman amphora was the plastic bag of its day so there's lots of stuff like that all over the Med, could it be part of a lid?

Aru, I been working at that now for some 18 years, have more-or-less given up but admire those few a2k'ers who know how and have the patience to actually perform it

I keep asking Mgmt to find a better way....

Meanwhile thanks once more to Ed or Oss or whoever it is providing that occasional instruction sheet. Trouble is it 'tains a lotta tech terms, would take Your Average Clod (me) an hour to actually perform

Guess: A glossy black quartz (might recall the name later) with inclusion of beautiful gloss white opalite. Man, help