A new carbon crystal named carbolite has been synthesized by quenching high temperature carbon gas on a room temperature substrate. The crystal has a density as small as 1.46 g/cm(sup 3) and is transparent for visible light. The crystal structure is hexagonal, and the dimensions of the unit cell are 1.193 nm in the a-direction and 1.062 nm in the c-direction. Along the c-axis, a parallel array of carbon chains is proposed. The array is made up of a triangular lattice in which the interchain distance is 0.344 nm and the mean interatomic distance within a carbon chain is 0.133 nm. The former value is close to the van der Waals distance between the honeycomb planes of graphite, and the latter value is close to the C-C bond length in the honeycomb plane. Intercalations of potassium, sodium, and iodine atoms are performed.