Clusters of airborne SiC fibres from the SiC industry have been studied by scanning and transmission electron microscopy (SEM, TEM). These fibres are produced as an unwanted side product during the industrial manufacturing of non-fibrous silicon carbide. It was found that the complex morphology seen for clusters of SiC fibres can be explained on the basis of the crystal structure of the fibres. By use of electron diffraction (ED) and high resolution electron microscopy (HREM) it was found that the SiC fibres can be described as needles based on face centred cubic structure (space group F (4) over bar 3m and a-0.4385 nm).The needles are covered by a thin amorphous layer of carbon. The needles contain a high degree of stacking faults and twinned areas. No long-range order of a hexagonal structure as a result of stacking faults was found. The SiC needles grow along the < 111 > directions.The existence of equivalent < 111 > directions in the cubic structure, separated by an angle of 70.52 degrees, explains the most common angle found between branches and the parent needle. Single and double twinned areas in the cubic structure have been found to produce a second and third set of angles between branches and a parent needle. The second set of angles is 38.94 degrees,43.31 degrees,55.53 degrees, 56.25 degrees and 66.16 degrees.One example from the third set is the angle similar to 83 degrees (97 degrees).These parent needles with branches may be significant to the toxicological effects of the airborne SiC fibres. (c) 2005 Springer Science + Business Media, Inc.