Physical Appearance and Location
Because of its proximity or location upon rocks and its dark coloring, the moss or mold covering stones became known as rock ash. Most often found in wet or damp places, like riverbeds, rock ash has an almost webbed appearance.
Commerce and Art
Due to its consistency and strength, rock ash is used for very many day to day purposes. If used by scribes, it can be made into a dark pigment, usually black or grey. It has also been sought after for its use as incense.
Though it is used in small doses as harmless odors, it can be brought together in higher concentrations to create flames and smoke. Typically, this chemical reaction can have a slightly volatile reaction.