The Jacobsville Sandstone, usually a beautiful rusty red color, is colored by hematite, which occurs as tiny, rusty fine-grained iron oxide.  We know that this hematite formed after the rock was deposited, from water that flowed through the pores.  Within the white areas there was material that reduced the availability of oxygen, which did not allow hematite to form. Geologists suppose that this could be organic material, produced by organisms.  If so these are ancient fossil remnants, perhaps the result of cyanobacteria. The spots are called reduction spots.

The Jacobsville used in many buildings contains more homogeneous red color.  This came from thick red layers which were quarried.  In many places the Jacobsville is quite variable, and this rock made for weaker but decorative masonry, such as the Powerhouse.