Download Gemstones and Their Origins by Peter C. Keller Ph.D. (auth.) PDF

By Peter C. Keller Ph.D. (auth.)

Each gem deposit-whether of basic beginning within the dad or mum rocks; or secondary as alluvial placers in valley flooring, river gravels, or the sand of oceanic cabinets­ provides an eloquent chronicle of the Earth's existence tale. It finds to the professional the prodigious strategies which shaped the current crust of our planet, of which this quantity discloses a small yet interesting aspect. The fabrics of the Earth's crust are the rocks. during this ebook, the writer expounds on how they have been shaped, why they altered, why they grew to become the cradles of useful gem stones, how they're labeled, and the way they're now exploited by means of guy. What initiates the expansion of gem stones? How do they crystallize? Why do gems of an identical species, originating from diverse assets, fluctuate? What reasons the incidence of sorts? Why do diamonds, in contrast to different beneficial stones, ensue now not close to the Earth's floor in its crust, yet deep down underneath it within the higher mantle? those are just some of the entrancing matters mentioned during this enlightening quantity. The reader learns that the Earth is strangely alive and changing constantly-sometimes via sluggish and equable alterations and from time to time by means of violent and large cataclysms, occasions from which gem stones issue.

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This deposit in the Andes Mountains of central Colombia, 60 miles north of the capital city of Bogota, has yielded the finest emeralds in the worldfor more than 400 years. Pegmatites, granitelike rocks with very large crystals, produce more kinds of gemstone than any other type of deposit. A pegmatite forms when the water-rich portion of molten granite is squeezed into a fracture in the solid surrounding rock. As the pegmatite liquid cools in the fracture, it begins to solidify at the outer walls first and then toward the center.

Found in 1922, it weighs about 50 carats. Other famous Lightning Ridge opals include the Empress, Black Prince, Pride of Australia (226 carats), Crystal Princess, Flame Queen, Pandora (711 carats), and Light of the World (252 carats) (Bancroft, 1984). Other opal-producing areas have also produced noteworthy gems. One of the largest uncut gem opals was the Noolinga Neera, an 86-ounce mass found about 4 meters below the surface by a group of Australian Aborigines at Andamooka. It was cut into a 205-carat oval stone (Scalisi and Cook, 1983).

Opal, South Australia's Gemstone. Geol. Survey of South Australia Handbook 5. D. J. Woolman, Eastwood, S. Australia. 157 pages. Connah, T. H. 1966. A prospector's guide to opal in western Queensland. Queensland Government Mining Journal 6723-39. Croll, I. C. H. 1950. Opal industry of Australia. Bureau of Mineral Resources Geology and Geophysics (Australia) Bull. 17:7-47. Darragh, P. , A. J. Gaskin, B. C. Terrell, and J. V. Sanders. 1966. Origin of precious opal. Nature 209:13-16. David, T. W. E.

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