These pictures are of an Atrypa sp. (Hall, 1862) brachiopod fossil. It was found in the Genshaw Formation at Carmeuse Quarry of Rogers City, Michigan, USA. The brachiopod lived in the Devonian Period (Givetian age). In September 2011, Dave wrote about another brachiopod from this area which is called "Blue Beds". The fossil has a blackish-brown color. Dave speculated that it might caused by hydrocarbons (bitumen, tar, or oil). See his post at Views of the Mahantango blog here.
