an unusual mirror

 There has been this mirror in my bathroom for a while. It's a rather small room and I wondered if the mirror made it look bigger so I decided to take the mirror down to see. It was surprisingly heavy. I guessed at least 20 pounds. I've lifted other mirrors before and they were much lighter. I even lifted two other mirrors in the house off the wall to check. Not that heavy. I went and got a scale and I was pretty close. Mirror was 25 pounds. I wonder what it's made of. From the outside it appears to just be glass and wood.