This artifact is small - only about an inch at its longest, as you can see below:
It is made of stone, and all four edges of the rectangle/prism have been worked and shaped. The stone from which it is made is dark grey, almost black, in color. At the risk of giving too much away, I will add one more clue . . . this particular type of artifact has been found on archaeological sites all over the state of Illinois.
Post your guesses on this blog in the comments section or over on Facebook, and we'll follow up soon to reveal this mystery artifact. If you'd like to take a closer look, this object will be on display in the lobby area of the museum, next to the previous mystery artifact, a kitchen tool called a salamander. Come on out to the museum and check out these cool artifacts!