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Unique Lightning Ridge Black Opal Photo by Wood's Stoneworks and Photo Factory on Flickr |
Lightning Ridge Black Opal it is like lightning bolts that flash and
change as it moves. Lightning Ridge mine site in New South Wales,
Australia.
Colour: Colorless, white, various
Hardness: 5½ - 6½
Lightning Ridge black opals are the most valuable in the world. Lightning Ridge is one of the few
places in the world where the precious and highly prized black opal is found. Unlike other opal, the black
opal contains carbon and iron oxide trace elements, producing a very dark stone which has hints of blue,
green and red play of colour.
Overlying the Cretaceous sedimentary rocks are sandstones and conglomerates that were deposited by streams and rivers in the Tertiary period, about 15 to 5 million years ago. Many of these younger rocks have hardened due to weathering processes to form silcrete and are commonly quarried for road materials.
Host rocks contained a variety of voids formed by the weathering process, which leached carbonate from boulders, nodules, fossils, cracks, hollow centres of ironstone nodules and horizontal seams. Most opaline silica deposited is common opal (or potch). It does not show a play of colour. Opal also fills pore space in sand-size sediments, cementing the grains to form deposits known as matrix or opalised sandstone.