A defect-induced peak at 328 cm−1in the infrared absorption spectrum of type Ia diamonds is confirmed to belong with the other absorptions (in particular, the B′ localised mode near 1370 cm−1and the D component of the lattice vibrations) which are associated with the {100} platelets found in these crystals. It is suggested that this absorption and other weaker absorptions found in its vicinity may be due to the bending vibrations of atomic bonds in the platelets.