|MadSci Network: Earth Sciences|
Based on the photo, your description that the rock is denser than might be expected, the fact that it has gold holes all the way through it, and the fact that it is not magnetic, I might make the following guess. I think you may have a solid block of iron pyrite (an iron sulfide mineral) also known as fool's gold. The bulk of it (the black part) may be pyrite coated with a thin layer of hematite (an iron oxide mineral) and the golden part might be where the outer coating has worn off by erosion or chemical action. For a more certain identification, you could take this rock to a local science museum or college and ask for a geologist to take a look at it. With the rock in her hand and the ability to run a few quick tests, she could give you a much better answer. Sorry I can't nail this down for you - pretty cool rock, though!
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