Mineralogy of microbial fossil-like textures in the Precambrian Marble Bar chert and Gunflint chert

Examining two Precambrian chert samples in which microbial fossil-like structures have been reported, textures of the microbial-fossils or similar components were mineralogically described. The Gunflint chert of 1.9 Ga and the Marble Bar chert of 3.5 Ga were used. Microbial fossil-like textures in the Gunflint chert were composed mineralogically of three different parts: the core, middle and outer rim. Among them, the inner core consists of apatite, having a slightly irregular shape. It cannot consistently be confirmed that this is biogenic but these mineral textures are an important factor, possibly supporting the origin of biogenesis. In the black part of Marble Bar chert, carbon materials can be found, covering rounded quartz grains in TEM observations. HRTEM examinations show that the black part contains not only amorphous organic matter but also low crystalline graphite structures.