Spherical groups with a radially fibrous structure and bristled with crystals on the surface are not uncommon.

It forms soft, dark brownish-black masses with a confused fibrous structure.

They may also occur as stellate (star-shaped) groups, or encrustations with a bladed or fibrous structure.

Exposure to long periods of low relative humidities (below 40%) can cause leather to become desiccated, irreversibly changing the fibrous structure of the leather.

Other examples of felted material in animal structures include fibrous structures coating the integument of some insects.