Readers send me the nicest things. The other day's email brought with it a photo of a large collection of pieces of ironstone, of a quality I don't see in my part of the world. So it's now in the gallery of sedimentary rock types along with a description of its three main types.
This type of ironstone is almost always found in bits and pieces rather than big-ol' beds like sandstone and shale. But it's nice to have the name handy when you find it.
Ironstone courtesy Joey Gabaldon