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A cautionary tale about a little-known type of non-nacreous calcareous concretion produced by the Magilus antiquus marine snail
Thomas Hainschwang, Thomas Hochstrasser, Irka Hajdas and Wolfgang Keutschegger
Abstract: Four most unusual objects represented as 
gastropod-shaped non-nacreous pearls (calcareous concretions) were analysed at the GEMLAB laboratory by standard gemmological and laboratory techniques. They were consistent with natural non-nacreous pearls, but these methods did not provide unambiguous proof that the samples are or are not unusual fossilized gastropods or something else. Therefore the objects were subjected to scanning electron microscopy and finally to a method only rarely used in the gemmological field — 14C age determination. Results were still inconclusive until consultation with malacologists and conchologists led to the conclusion that the specimens are natural and belong to the species Magilus antiquus. Their terminology is discussed.
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