Challenged by @mcsiegle challenged me to do opposites but not in a diptych.
The chalk was picked up on a recent walk.
So for opposites:
Hard & soft
Edible & not too tasty
People & personalities are often described as chalk & cheese.
I have never heard that phrase before so it was a good education and I think you did a remarkable job of responding to that challenge with this photo. The light and shadows are excellent
Like @grammyn I also was not familiar with the saying "like chalk and cheese" but knowing that now, I'd say you aced this challenge! Nicely composed picture with the two at right angles with each other and more than one different opposite. Mission well accomplished!
Now for ecology's sake you have to return that lump of chalk back where you found it!!