We performed transmission electron microscopy studies on dynamically deformed pure cobalt. The results show that the twinning plane of the most common twinning mode in hexagonal close-packed metals is non-coincident

that is

the twinning plane of the parent and the twin does not coincide. Statistical measurements show that only 44% of the twins have a misorientation angle close to the theoretical value of 86.3°

and 79% of the twin boundaries (TBs) deviate from the twinning plane. Thirty-two percent of the TBs deviate from the twinning plane by more than 40°. These results indicate that the twinning significantly departs from the classical twinning behavior.