A diamond element (10) having a convex surface is disclosed, the convex surface including a spherical segment for which the maximum peak to valley deviation from a perfect spherical surface is less than about 5 μm. The diamond element (10) may be a solid polycrystalline diamond material and/or may comprise base material which is coated with diamond. Alternatively or in addition, the RMS deviation from a perfect spherical surface may be less than about 500 nm, or the RMS roughness less than about 30 nm. A diamond element (10) with a radius of curvature less than about 20 mm is also disclosed. In one aspect a diamond element (10) having a conical half-angle greater than about 10° is described. Diamond elements (10) of this type are intended for use as metrology tips.