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Volume 5, 2010 - Number 2
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AGATES FROM GURASADA, SOUTHERN APUSENI MOUNTAINS, ROMANIA: AN XRD AND THERMOGRAVIMETRIC STUDY
Ciprian CONSTANTINA1 & Terry MOXON3
1North University of Baia Mare, 62A Dr. V. Babes Street, 430083, Baia Mare, Romania, cconstantina@yahoo.com 255Common Lane, Auckley, Doncaster, DN9 3HX, England AGATES FROM GURASADA, SOUTHERN APUSENI MOUNTAINS, ROMANIA: AN XRD AND THERMOGRAVIMETRIC STUDY Full text
Abstract:
A suite of agates from Gurasada, Romania have been characterised using powder X-ray diffraction, thermogravimetry and density determinations. A comparison of agate data from Gurasada with 14 other world-wide regions reveals discrepancies in the Gurasada agate information. The crystallite size, density, defect-site water and moganite content demonstrate that these agates can be characteristically divided into two groups. One group reveals properties that are consistent with a contemporaneous formation around the age of the ~75Ma old host. Host rock bentonitisation is a likely silica source for the second group of agates that have apparently formed ~ 55 Ma later. Additionally, a number of the Gurasada agates contain cristobalite that exists as a white rind and within the agate structure.
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