These images are of Polyaxons strongylasters sponge spicule fossils. They were found trapped in cavities in Halysites coral fossils and a microscope is needed to see them. The images have a 1-2mm field of view.
The fossils were found in the Louisville Limestone of Jefferson County, Kentucky USA. This layer dates to the Silurian Period.
Thanks to Kenny for images and discovering them with his microscope.
