Those are stones allright! You'll probably find that what you get out varies with each flush. Some are bright green inside and outside and softish (newer stones?)...and some have crusty green or golden outsides with green insides (slightly harder)...they can be almost black or even white. The calcified ones are the only ones that show up on the ultrasounds...you need a collander in the toilet for sure, if you want to catch those ones...