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[marco campos-venuti]

Years ago I cut a beautiful clear opal cabochon with a beautiful well-centered black dendrite. The best quality of that cabochon was that it was from Cabo de Gata, Almeria, Spain a little-known location for gemological materials. After 12 years something happened to my dendrite. Can anyone suggest what happened? The photos are taken with the same camera and in the same microstudio without any processing.

[Roy Starkey]

Hi Marco
Interesting question. It looks as if the iron (?) oxide / hydroxides may have undergone some form of slow hydration through uptake of moisture from the atmosphere and diffused through the microstructure of the opal.
Best wishes
Roy