Preservation Pop Quiz

Quiz on a Friday?! That takes me back to high school; I always had quizzes on Fridays. Thursday nights were never relaxing. But, you are not being graded on this. Take a guess.

What is this architectural material?


What can you tell me about? Where is it found? How old is it? What brought you to this conclusion?

(Yes, I will post the answer.)

EDIT: A better photograph.

Scale: roughly 3"x6".