Talking about darker opal backgrounds wouldn't be complete if I didn't mention "chocolate" opals. Obviously the name was chosen because of the rich dark and milk chocolate colors of certain precious opals found in Ethiopia. Modern man didn't really take notice of these lovely stones until the late 1990s; until then, Ethiopian opals had been known to be an unstable stone that would quickly craze. Lapidaries and jewelers have now figured out about how long it takes an Ethiopian opal to cure after it has been dug out of the ground, before they attempt to cut it. Chocolate opal can vary to a brownish-peach background and has awesome color play in deep, electric hues including green, blue, orange, yellow and red; some even flash a neon indigo or turquoise! Ethiopian opal forms in nobbies encased in rhyolite. These geode like formations most often contain just potch, only about 20% actually contain opal with play of color, therefore triple A grade Ethiopian opal is rare and can cost up to $200/ct for a faceted stone or cabochon. Believe it or not, archaeologists excavating in Kenya found very early tools, rather than jewelry or ornaments, made of this opal, suggesting that opal was mined in Africa before Australia, but who really knows?
Very difficult to photograph, these are precious dark chocolate opal cabochons (front) and "root beer" opal rough (back) from Ethiopia. Private collection, Dale Armstrong.