A copper ore vein with one raw copper block and no other ore anywhere near it. It appears to be a single block vein, which does not look correct and defeats the point of having "larger veins" to make mining more interesting. I found it while exploring a cave, it was exposed to open air. I have included a screenshot of the F3 screen at the location facing said block. I have used the command </fill ~10 ~10 ~10 ~-10 ~-10 ~-10 air replace stone> to show the absence of ore around it while standing next to the block.

The seed for the world is: 4946792059427890619