ALWAYS WEAR GLOVES WHEN HANDLING ROUGH GLASS!  This chunk really looks like a piece of art to me. Made in the Pittsburgh area of PA no later than the 1940s, but possibly much older. The specific PPG plant that these items are from opened in 1887 along the Allegheny River in Ford City, PA. It actually turned the town into a boom town for quite some time. These pieces came from a man who worked in that plant in the 1940s. PPG has an extensive history in the United States. If you buy this piece, you're buying a piece of history. This piece has black parts and dark green parts and clear parts, and you can see where the glass was once molten and settled. Requests for more photos and questions are always welcome!