This is the source of the famous Ethiopian Chocolate Opal, though the precious opal found here can come in different colours. There are also plenty of specimens with common opal and without opal at all, instead being filled with a simple agate. My specimens are all of this last kind. I have always been put off buying the actual opal thundereggs because the prices are painful given that they are all too often broken rather than cut. One day I might get one, but personally I find the agate specimens just as interesting.