What the close-up? #3

Interesting. So #1 was too easy, and #2 proved too ambiguous and difficult. I agree that "grains of some powdery stuff" was about as close as anyone could reasonably get to the answer. Hopefully #3 will strike some balance between too trivial and too impossible.

Can you identify what this is?

Answer

It was pretty clear to our contestants that this was the bottom of a glass bottle. I am in Spain, however, so I'm surprised that no one correctly guessed that it was a wine bottle.

by erikrasmussen, on Flickr")

Ridges on the bottom of a wine bottle.

Due to, shall we say, family matters, this feature will be discontinued for an unspecified amount of time. Thank you to all who participated, especially Simon, who participated in every post.