Mono red oak on rock

You'll have to take my word for it that this is a Red Oak leaf (though it is actually brown in color - go figure).

When I moved to the USA, one of the things I had to get used to was the fact that every size of rock here is just called a rock. Sadly, my brain has lost some of its former knowledge of words for different sizes of rock: pebble; boulder etc... Feel free to refresh my memory by leaving a word in the comments :)