Bornite, also known as Peacock ore, is a mineral that tarnishes to different colors, ranging from blue, yellow, and purple. This is the first sample of it I have found locally, right in my local shale pile. I have a feeling that I will be finding more of it now that I have identified it and know what it is. While we focus only on local fossil creates, the local geology is very important as well.
The chemical structure is Cu5FeS4. This indicates Copper, Iron, and Sulfur. The mineral is considered a sulfate. Apparently, you don’t find it coating fossils locally. This particular specimen coats a piece of shale no wider than 3 inches and appears very brittle. The surface is fascinating and I have provided several microscopic views below. The crystallization of the substance creates some odd geometric shapes.
These examples were found below the Brush Creek limestone, in the Glenshaw Formation.
Bornite 
