Based on the topologies proposed for zeolites, six metastable semiconductor carbon allotropes with band gaps of 2.72-3.89 eV are predicted using ab initio density functional calculations. The
hardnesses of these allotropes are about 90%-94% that of diamond, indicating that they may be superhard materials. We also present simulated X-ray diffraction spectra of these new carbon allotropes to provide a basis for possible experimental observations and synthesis. These new carbon structures with a range of band gaps and with hardnesses comparable to diamond could be potential targets for the synthesis of hard and transparent materials.