Why doesn't diamond show up in X-ray imaging? Diamond is the hardest substance ever known, and as we know, X-ray radiation is produced when a cathode ray of high frequency hits a very high atomic mass target. But I am amazed: why doesn't diamond show up in X-ray imaging? Exactly how and to what extent diamond shows up in x-rays depends on factors such as type of x-ray apparatus, size of diamond, orientation and so on.