One day I really must replace the tutorial on seams and cutlines which I accidentally deleted.
For ID purposes, I find the most useful views of patches and rainbow/rainbo-style marbles to be the seams. I'm going to start pulling up different marble types from my basement and start working on that new tutorial today. In the meantime, here is an example of marbles posed to show off one of their seams. Such marbles usually have another seam on the opposite side, which can also be useful to show. Some marbles have a little scoop seam on one end and a V-shaped seam on the other end, for example, and that is a big clue.
I might need to retake the picture of the top left one here, I might want to pose that so it will look more like a V-seam. I need to look at it more closely. Will do that as I try to bring up nice representatives of marbles with this style of cutlines.