How rare are gemstones??

You know there is a thing with key fragment that if you have a x amount of wins(I don't remember how many wins) then you are guaranteed to get one to avoid bad luck. Can't the same happen to gemstones but just rarer? I really don't understand what is the % of getting a gemstone from a chest. Some of my friends who play rarely have up to 3 gemstones, meanwhile I play a lot compared to them and I haven't gotten a single gemstone yet. I also don't want to throw money onto the screen to get them.(I have bough 20+ chests for rp too). I bet if I were to open chest with rp I'd get all the possible skins before I'd get 10 gemstones.