What's the gray stuff?

Just finished my second flush. Not as bountiful as the first one, but still passed a huge stone which was oblong over 3.5 inches long and over 1.5 inches wide. It was covered in green globs but was wrapped around gray spongy stuff. Then later passed another one but it was long and thin, like a piece of rope also cover in green globs. Then about 5 hours later, passed a bunch of gray spongy stuff. Does anyone know what the gray matter is? And should the stones be long and thin. Could it have been a parasite that the green stuff was formed around? Tweet