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Bristol Diamonds
Bristol Diamonds are not actually diamonds but quartz crystals found in geodes, geological rock formations which occur in dolomitic conglomerate found in the Avon Gorge in Bristol, England. Their origin lies in geological processes of the Triassic period, about 250 to 200 million years ago.
The Bristol Diamonds became popular novelties for visitors to the spa at Hotwells, Bristol, during the eighteenth and nineteenth centuries. Diarist John Evelyn and travel writer Celia Fiennes were amongst those who described them. In popular culture they became a synonym for something bright but worthless.
==Origin==
Dolomitic Conglomerate formed during the Triassic period (about 250 to 200 million years ago) in the Bristol Avon Gorge as a result of clays mingling with rock debris scree which had formed against the Carboniferous limestone cliffs of the gorge. The geodes containing the Bristol Diamonds are frequently found in this conglomerate, in the areas of Bridge Valley Road, Leigh Woods, Sea Mills and St Vincent's Rocks. The geodes were formed from quartz, either megaquartz or fibrous quartz, the diamonds themselves resulting from the dissolution of nodules of anhydrite leaving a void which allowed the silica crystals to grow.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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