Jo Ellen

Nantes Université

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R. Nicole Howie

Medical University of South Carolina

James E. Shigley

Gemological Institute of America

A. A. Levinson

University of Calgary

Jana Miyahira

Gemological Institute of America

Elise Misiorowski

Nantes Université

Patricia Gray

Nantes Université

Maha Demaggio

Gemological Institute of America

Mary L. Johnson

Park Nicollet Clinic

Carol M. Stockton

Nantes Université

Juli Cook-Golden

Royal Oak Community Coalition

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Gemological Institute of America

Nantes Université

University of Calgary

Universidad de Londres

Royal Holloway University of London

Missoula County Public Schools

Institut de Recherche en Génie Civil et Mécanique

Global Engineering and Materials (United States)

Royal Oak Community Coalition

Ithaca College

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Gemological Abstracts

Gems & Gemology (1994)

Charles Ashbaugh Ill Andrew Gia Santa Monica Jo Ellen Cole Gia

T h i s report describes a procedure for determining whether v a i ~d i u n ~ is present in be~yl andl by extensionl how to distinguish green beryls colored by c l l r o ~n i u ~n froin those colored by vanadiuin.The first step is to record an ESR (electron spin resonance] sl~ectruin of the stone in question and compare it to a si~~lilarly oriented reference spectruin of a gamma-irradiated Biroil synthetic emerald.If there is a clear inatcll wit11 the latter's vanadiuin pealzs!no further testing is required.When the results are ambiguousl however! the test san~ple is gamina-irradiated, Such treatment will reportedly increase the intensity of absorption features attt-ibutable to vanadiuin so that they can be detected when another ESR spectrum is run.Using this tecllniquel the authors detected vanadium in three eillerald specimens froin Colon~bia.They also found that one sainple each froin Brazil and Zainbia did not contaii~ vanadiuin.RCK Snioky moolistone: A new nioonstone variety.H. Harder, /

10.5741/gems.30.4.282

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Gemological Abstracts

Gems & Gemology (2005)

A. A. Levinson Christopher M. Breeding Maha Calderon Jo Ellen Cole Vista

This article suggests new terminology to describe the banding of agates, in order to alleviate the confusion caused by previous descriptors that have no direct correlation to genetic implications.One ambiguous term, Uruguay banding, has been used to describe the straight parallel banding that often occurs in the lower portions of agate-containing vesicles from continental flood basalts.Confusion results because agates with this type of banding are called Uruguay agates, a term that some use to describe any agate from Uruguay.The author suggests using gravitational banding to refer to all agate textures caused by the force of gravity, which in this case applies to the deposition of relatively thick bands of coagulated silicic acid.The term adhesional banding is suggested as a replacement for terms such as concentric, common, normal, and fortification banding; these all refer to the thin layers of silica that adhere to the vesicle walls and form concentric rings or zones.Both types of banding commonly occur in agates formed in continental flood basalts from many locations worldwide.Several factors, including the amount and thickness of the lava flow, the temperature and humidity of the region, and the amount of CO 2 in the atmosphere, all contribute to the formation of the agate-filled vesicles.A suitable lava thickness will facilitate a slow cooling rate, which allows for the coalescence of numerous gas bubbles into larger vesicles and voids.Conversely, cooler atmospheric temperatures will inhibit vesicle formation.Sufficient rainfall will provide enough water for Gemological

10.5741/gems.41.3.285

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Gemological Abstracts

Gems & Gemology (1994)

Charles Ashbaugh Ill Andrew Gia Santa Monica Jo Ellen Cole Gia

10.5741/gems.30.3.207

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Gemological Abstracts

Gems & Gemology (1997)

C Fryer B Oa A Rd David Charles E Ashbaugh

The question of the cycling of carbon through the Earth's crust and mantle is one of great interest with regard to the origin and evolution of diamonds.Carbon-bearing phases in the mantle include calcite and dolomite, as well as diamond, graphite, silicon carbide, dissolved methane, carbon monoxide, and carbon dioxide in fluids, and "carbonate components" in magma.The phases that form are a function of the availability of oxygen, as well as carbon, in the mantle.Evidence has been accumulating that carbon from the crust is recycled deep into the mantle by subduction,-an important destination for this carbon-other than in diamonds-is the igneous rock carbonatite.The carbon isotopes in carbonatites do not match those of either marine carbonates (e.g., from coral reefs) or organic carbon (e.g., from plant debris); however, these isotopes are similar to those in peridotitic diamonds.From the study of trace-element distributions, especially of ultramafic xenoliths in carbonatites, the author concludes that these rocks probably result from repeated interactions of carbonate-rich mag-matic fluids with restricted volumes of metasomatically altered mantle rocks.Several influxes of carbon-rich magma have been implicated in the formation of diamonds at the Premier mine, and of coated diamonds from Africa, Siberia, and Australia.Carbonatites are uncommon in the Earth's crust, but this is probably because the mantle "soaks up" most batches of carbonate-rich magma, and only a few manage to reach the surface.MLJ S So ou ut th he er rn n A Af fr ri ic ca a' 's s o of ff fs sh ho or re e d di ia am mo on nd ds s. .Mining Journal, London, January 26, 1996, p. 63.An increasing share of South Africa's diamond production comes from offshore deposits; for instance, in 1994, 31% of the country's total output (407,000 carats out of 1.31 million carats [Mct]) came from offshore, and 1995 production probably exceeded 500,000 carats."Huge quantities" of gem-quality diamonds have been deposited

10.5741/gems.33.1.73

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