Summary: The symmetry of diamond is still disputed, and is usually regarded as 4∕m3¯2∕m or 4¯3m. The (rare) development of tetrahedral morphology has been cited in favour of the lower symmetry. A tetrahedral crystal c. 4 mm edge-length was studied for evidence relevant to this controversy. Three similar quadrants have nearly plane tetrahedron faces, each surrounded by six curved surfaces belonging to forms {hkl}. The fourth (unique) quadrant, containing (II¯I¯), differs topographically. In the three similar quadrants the tetrahedron faces exhibit coplanar banding of trigons parallel to (II¯I¯), and the curved surfaces have striations parallel to it. The banding and striations are interpreted as stratigraphic etching of nitrogen-rich layers parallel to (II¯I¯) in a type I diamond. Slip, and apparently polygonization, occur in the unique quadrant. The three similar {I I I} faces were formed by cleavage, and the curved surfaces, banding, and striations by subsequent dissolution. It is probable that (II¯I¯) was part of an original octahedral surface, since tetrahedra of diamond are so rare. The tetrahedral morphology does not necessarily indicate that this crystal belongs to class 4¯3m. The doubt cast upon tetrahedral morphology (and the inferred twinning on {100} or about <100>) as evidence in favour of lower symmetry strengthens the case for assigning diamond to class 4/ or about <100>) as evidence in favour of lower symmetry strengthens the case for assigning diamond to class 4∕m3¯2∕m.