MYSTERY METAL

Pic #2, large chunk, right hand side - looks to be a circular oil galley hole from a bearing, with only 1/4 of it remaining.

Can you remove the tarnish?

If it’s not a bearing, looks as if it’s just timing cover gasket scrapings. Which would explain the rock. All the junk from a timing cover change falls into the oil pan. A dirty truck collects a lot of rocks.