I bought a 1 ct tanzanite and diamond ring at Riddle’s Jewelry (a local store in the mall) about 2 years ago and it seems as if the tanzanite has developed a dark "shadow" in over 1/3 of the stone. What causes this and can it be fixed? Was it something in the jewelry cleaner that I used (an ammonia based cleaner I bought at Walmart)? I am just sick about this as it was 00 for the ring and I don’t have the receipt anymore. Just curious if anyone could help. Thanks!