“...The finding location Star Mountain Opal Mine is on the area of the Crowley Ranch in the Malheur County in Oregon. In the Thundereggs occuring here opalite (i.e. common opal without opalizing ) represents the most frequent filling component. In addition, agates partially with pseudomorphs and possibly with a “Tilt” ( tilting of the agate-banding due to tectonic events) occur here too...”

From the presentation-programm “These Fabulous Thundereggs”, published by Doug Moore, Stevens Point, 2005