Lavas of the Kamchatka volcanoes store cubic-octahedral diamonds identical in morphology and structure to synthetic crystals, and their natural origin is doubted. Judging by published data, the diamonds discovered in the Tolbachik lavas are similar to synthetic diamonds made by different producers, and the analyzed samples rather result from contamination with synthetic material. Ophiolite-hosted diamonds reported from Europe, China, Mongolia, and Polar Urals look like the Tolbachik diamonds and are of the same type. The similarity between crystals coming from geologically dissimilar objects indicates that contamination may occur in those cases as well. Thus, diamonds found in unusual hosts or geologic settings require careful checking. These findings have to be reproduced repeatedly in other in situ samples and approved by independent experts; with all respect to the priority of the first finders, the sampling sites should be open to many researchers, especially the respective specialists. The inevitable disproval of false diamond findings is discouraging and discredits the true discoveries. Possible contamination with synthetic or natural material from cutting tools has to be excluded in all newly found diamonds before claiming their natural origin.