To explore the possible existence of boron clusters without carbon analogs, we study B-84 cluster as a prototypical system by ab initio calculations. Structures of several isomer forms of B-84 are optimized. Among these isomers, a group of amorphous (disordered) structures are found to be the most stable. Different from the high-symmetry isomers, the amorphous B-84 clusters are more stable than the fullerene B-80 in terms of cohesive energy per atom. These amorphous structures can be distinguished from other high-symmetry structures experimentally via, for example, infrared spectra. The radial and angular distribution functions of amorphous B-84 structures are more diffuse than those of high-symmetry structures. On the basis of these findings, we propose that amorphous structures may be generic for boron and dominate boron clusters in a range of cluster scale.