Monolithic building block

A monolithic building block (10) includes a light phase (18) and a heavy phase (16), and has a density gradient along at least one direction of the block (10). A differential density between two spaced slices of the block taken in the same direction may be 300kg per cubic meter. The block may have different compressive strength in the two slices, with a ratio of at least 3:1. Thermal conductivity of one of the slices may be at most 0.36W/mK ands a thermal mass ratio of the slices may be at least 2:1. The block may include light aggregates selected from, polystyrene, hemp, cork, expanded glass, light expanded clay aggregate, pumice, perlite, scoria and vermiculite. The clock may include heavy aggregates selected from sand and crushed stone. The block may be moulded from slurry which is vibrated to stratify the aggregates.