Klondisco

Hello, I have a mysterious rock I found a long time ago in my yard. I found it in my yard a couple years ago. The rock looks like nothing in the area, and I just want to know what it is. My first guess was obsidian, but my Earth Science teacher said he had no idea, and that it wasn't obsidian. It looks like it is starting to rust on the top. There are white specks on it, and it looks melted. Here are some pictures of it. I can post more if it would help. Thanks in advance! EDIT: Found in Wisconsin