In my opinion, diamonds in the image are often the consequence of the lens refraction. 

Judging from the light/ shadow distribution, in this image the Sun is above the right upper image rim. The diamond's left and right top and left bottom edges are blurred so as they were above the more thick part of the chemtrail and right bottom one, being in less clouded area, is somewhat sharper.

From this it can be assumed that what is captured is the object above the chemtrail clouds. 

If it was a lens diffraction effect, all edges should be equally sharp/ blurred and their sharp/ blurred position distribution would not mach that of chemtrail clouds so precisely.

Note also formidable display of a freshly dumped chemtrail in the middle of the picture. 

It is remarkable how some military pilots can, on a discussion boards, with a straight face state that they believe that there are no chemtrails at all and that what everybody sees are only normal contrails.

If this were so than Air Force would have been suffering from a major jet engine maintenance problems and F-16 and other similar vehicles would be falling out of the clear blue skies as stones.

And my car parked by a sea shore would not be so generously covered by chemtrail dust each day. 

Remember clear blue skies? I do not.