Fundraiser for Australian wildlife. Fire opals from Mexico. The varied and bright colours are natural. I have mounted these on small mirrors, which reflect light back through the opal.
The final photo shows examples of all the different colours and forms of opal that I have on my web site (at least until some sell). Just put "opal" into the search box to see them all.
Left: 1/2 inch (1.3 cm) diameter, 9/16 inch (1.4 cm) tall. $12