We decomposed acetylene by chemical vapour deposition in presence of FeCl2 vapours, which react with carbon radicals without thermal decomposition (500 degrees C). This produced a large volume of wool-like product around the FeCl2 reservoir, composed of semi-crystalline carbon fibres, with high conversion rate (40 mass%). Fibres showed remarkable morphology, with iron nano-rings belting their centres and mirror symmetry. Fibres were mono or multi filament (each filament belted with metal). Semi-crystalline fibres were readily transformed by thermal treatment into a large-angle conical structure with turbostratic piling along fibre axis. These observations suggest a catalytic growth on the inner wall of iron rings. (c) 2006 Elsevier B.V. All rights reserved.