California Claudia

Gemological Institute of America

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Russell Shor

Stornoway Diamond (Canada)

Keith Mychaluk

Gemological Institute of America

R. Nicole Howie

Medical University of South Carolina

Christina Taylor

University of Duisburg-Essen

Rolf Tatje

Gemological Institute of America

Wendi Mayerson

Gemological Institute of America

A. A. Levinson

University of Calgary

Sharon Wakefield

University of Duisburg-Essen

Gia Carlsbad

Gemological Institute of America

V.S. Dombrovskiy

Federal State Budgetary Institution "Center for Expertise and Quality Control of Medical Care"

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Gemological Institute of America

Royal Holloway University of London

Ithaca College

Parks Victoria

Nantes Université

Russian Academy of Sciences

University of Calgary

Stornoway Diamond (Canada)

Institut des Matériaux Jean Rouxel

Universidad de Londres

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Gemological Abstracts

Gems & Gemology (2003)

A. A. Levinson Jo Ellen Cole Vista California Claudia D Andrea

It is difficult to determine the chronological age of fossil resins by chemical analysis alone, because amber samples of the same geologic age may have experienced different chemical reactions and temperatures during their fossilization.This study was undertaken to evaluate the possibility of classifying ambers by thermal analysis techniques.Thermal analysis involves the detection of small changes in the weight of a sample as it is subjected to controlled heating.Two methods-thermogravimetric (TG) and differential thermogravimetric (DTG) analyses-were used for 13 amber samples of various ages (present day to Triassic, 225 million years ago) and eight geographic origins.Using the DTG method, all samples exhibited a main weight-loss event at about 400°C, but the exact temperature varied according to age (i.e., the temperature increased linearly with age).The results suggest that thermal analysis provides an additional way to characterize fossil resins.

10.5741/gems.39.4.351

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Gemological Abstracts

Gems & Gemology (2003)

A. A. Levinson Jo Ellen Cole Vista California Claudia D Andrea

The degree of crystallinity (i.e., crystallite size) of agates from 11 locations on five continents was determined by powder Xray diffraction analysis.These agates formed within vesicles (gas cavities) in volcanic rocks; the ages of these rocks were obtained from the literature.The author found a strong correlation between agate crystallinity and age of the host rocks.Over geologic time, ageing allows the crystallite size to increase.Accordingly, the determination of agate crystallite size should allow an estimation of the approximate age of the host rock, which can be used to differentiate known agate deposits (since each has a unique age).The same correlation was deduced between agate density and age of the host rock.These conclusions have several potential applications.For example, an agate "artifact" purchased in Idar-Oberstein was shown most likely to have originated from Brazil rather than Germany on the basis of its degree of crystallinity and density.However, for this technique to become an accepted gemological tool, a large database with crystallinity and age data for volcanic agates and their associated host rocks, from many localities worldwide, must be developed.This method is not currently applicable to agates occurring in sedimentary rocks.KAM Bright prospects for pearl culture in India! A. K. Sonkar, Infofish International, January 2003, pp.13-16

10.5741/gems.39.2.171

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