A method for forming a carbon fibrous structure having a granular part, to which a plurality of carbon fibers are bound, includes heating a mixture of a carbon source and a catalyst at a temperature between 800 and 1300° C. to produce a first intermediate, and heating the first intermediate to remove hydrocarbons, at a temperature between 800 and 1200° C. to produce a first product. The method further includes heating the first product at a temperature between 2400 and 3000° C. to produce a final product. The carbon source includes at least two compounds having different decomposition temperatures or a compound that can produce, when heated at a temperature between 800 and 1300° C., at least two components having different decomposition temperatures. The catalyst may include an iron-containing catalyst, which may be introduced into a reaction chamber in a gaseous state, without being deposited on a substrate.