I'm a kidney stone expert (not on the MD side, incidently). According to my urologist, oxalic acid is required to precipitate the most common kidney stone... calcium oxalate. Without the oxalic acid the doctor claims the calcium passes freely in the "wash". That's why one of the standard preventative treatments is avoidance of oxalic-bearing food, like spinach and other healthy leafy green veg, cola drinks, coffee, etc. and plenty of water/beer. I know that there is also a chemical preventative treatment but I can't remember what it was. Once the Doc prescribed this (two large horse pills per day) but I stopped taking them -- they passed whole and it was weirding me out! Allegedly whatever chem this was would bind with the calcium and take it out of the system.

I hope there is a chemist in the house that can continue to help chemically explain your phenomenon. But, it does kinda' sound cool... if the sparkles are in the right place.