March 17, 2004 — The millimeter-scale (.04 inch-scale) layers in the lower portion of this image is also hinted at by the fine notches that run horizontally across the sphere-like grain or "blueberry" in the center left. The thin layers do not appear to deform around the blueberry, indicating that these geologic features are concretions and not impact spherules or ejected volcanic material, called lapilli. Concretions are balls of minerals that form in pre-existing wet sediments.