White opal consists of silica spheres containing a variable percentage of water (8 – 12%) but unlike quartz, the silica is non crystalline and has solidified into a type of stone jelly. The material itself is almost colourless, and its play of colour, which embodies the entire spectrum, is caused by the irregular arrangement of rows of tiny spheres which produce this optical effect. In earlier times,
opals came from Hungary, and then early last century the opal fields of Australia were discovered and most of the world’s opal fields are from that continent.
Since opals are formed within the cracks and cavities of sandstone, many prospectors have destroyed a small fortune by striking a careless blow and thereby shattering what might have been a valuable opal ore within the boulder.
Discovered 1880’s Black opal has made Lightning Ridge famous. White opals are found in many parts of the world; Australia produces around 90% of the world’s opals’. Lightning Ridge is home to the very special dark variety, known as black opals and has the largest known deposits in the world.
The body tone of this variety can range between dark grey to jet black. Due to the body tone and the rainbow colours make the black opal stand out much better than lighter opals. Top of the range black opals can fetch prices up to £11000 – £12000 per carat.
Is the grass green variety of the mineral beryl; other colours of the beryl are aquamarine, morganite, goshenite and heliodor (yellow)/ Rich deposits of emeralds in Colombia were discovered after the Spanish conquest of South America. The deposits at Muzo are still being worked. In 1830 emeralds were discovered in the Ural Mountains of Russia.
Other sources include Brazil, South Africa, Pakistan and Zambia. The emeralds colour result from a trace of chromium, vanadium may be present. Egyptians held emeralds as a symbol of fertility and life. When held in the mouth, emeralds were believed to be a cure for dysentery, were worn to prevent epilepsy and was said to assist women in childbirth. Emerald was synthesized in 1937 and is currently made in the United States and appears very similar to natural crystals.
Sometimes called Mexican fire opal as it is mainly mined in Mexico and Honduras. The most important mines in the state of Queretaro discovered in 1835 are still producing today. The colour ranges from yellow and orange to brown to red. The finest stones display a vivid translucent to Sometimes called Mexican fire opal as it is mainly mined in Mexico and Honduras. The most important mines in the state of Queretaro discovered in 1835 are still producing today. The colour ranges from yellow and orange to brown to red.
The colour ranges from yellow and orange to brown to red. The finest stones display a vivid translucent to transparent burnt red orange combination, occasionally with iridescence. Opal fills cavities in sedimentary rocks, or veins in igneous rocks. It can form stalagmites and stalactites and replaces organic material in fossil wood, bone and shell. Although many fire opals are cut en cabochon some are faceted and set in rings the beautiful orange body colour gives fire opal its name Iridescence: An optical phenomenon which gives a rainbow effect from different atomic layers within a stone.