fire opal

The name opal comes from the Sanskrit upalas, meaning precious stone. The mineral is a hydrated form of silica without any crystallization in a specific system and therefore amorphous. Its formation is linked to the vagose waters coming from sandstones and produced by the alteration of feldspars into kaolin.
Following the gradual evaporation of these waters, the silica contained in them condenses into an aqueous silicate gel, which solidifies in the cavities, between the layers along the contact planes between clay lenses.
The bright shades from yellow to red of the fire opal are due to the presence of iron.
In the past opal was considered unlucky, this is a legend due to a story by Walter Scott (Anne of Geierstein). With the passage of time this belief has been overcome and opal enjoys all the admiration it deserves for its incredible beauty.