The surface is covered in numerous small, evenly spaced conules. The osculus, which are typically raised, range in diameter from 0.3 to 1 cm. The primary fibers are scarce and form at the ends of the conules through the merging of several fibers, often containing foreign particles. The secondary fibers have a diameter ranging from 0.002 to 0.0035 cm and create a tight network, especially near the surface. The color varies from a slightly yellowish white to black depending on the lighting, with a rust-like hue inside.