Summary: Previous statements about the common lamellar structure in orthopyroxenes are reviewed. New X-ray evidence is produced along with the results of optical examination of specimens from several localities. It is shown that the lamellae are composed of the same orthorhombic material as the main crystal and that the visibility of the structure is due to differences in extinction position between the sets of lamellae. These sets of lamellae have their a- and c-axes displaced relative to those of the main crystal in, or nearly in, the ca plane at angles up to about 10–15°. This structure appears to be due to deformation and is evidently formed during crystallization.