I was recently in Playa Del Carmen, MX and saw a ring as you described. I had 3 different jewelry shops try to get me to buy it. They called it simply "Maya stone". The ones I saw changed from a beautiful emerald blue/green when inside to a golden rose color when taken outside. They wanted $250 for it. I really liked it but couldn't see myself buying it for that much money so I walked away. Only one place said they could give a certificate of authenticity for it but still wanted $235 for it. They claim it has only been found and mined from 3 different cenotes down there in the Yucatan. They claim that there are only 3 other kinds of gemstones worldwide that change color like this. I have been trying to research it on my own to see if I could verify what I was told. I would still like to get one but I want to make sure it is authentic.