When taking photos for selling physical minerals I did not standardize the size. However, I see that the size should be standardized when adding to the eCryptonite collection.
Because I believe some of the buyers wish to print physical pictures, I do not want to use the standard PC formats where pictures are 4:3 or square. Also when taking pictures of minerals many would not fit into a 16:9 format. So I ended up that I will make the old-fashion 3:2 format, which was originally used for photos. That solution might also be easier for the ones who wish to buy standard frames.
I also focus on that the resolution on the pictures should be good enough to make big prints. I tried uploading the pictures to someone who prints, where the program gives a warning of how big I should make the physical print. However I tried to enlarge the pictures to my 55" TV Screen, and they look good in this format.
In the future, I will also inform you what size the pictures are, and also update the information about the previous ones.