Five Centuries of Mexican Pearls Star Garnets from Ilakaka, Madagascar The Springsure Deposit of Precious Opal Gemchecker Professional Valuation and Appraisal Module Corundum/Spinel Reaction Textures in Carbonate-Origin Rocks, Sri Lanka - Preliminary Observations

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FIVE CENTURIES OF MEXICAN PEARLS

Douglas McLaurin Moreno, Enrique Arimendi Castillo
Perlas del Mar de Cortz S.A. de C.V., Guaymas, Sonora, Mexico.

ABSTRACT
This review details the history of the Mexican pearling industry in the Gulf of California, and includes details of the development of the pearl culturing industry responsible for creating the Sea of Cortez bead nucleated cultured pearl. The history of the worldwide cultured pearl industry is given, and the pervading influence of the Japanese pearl culturing industry explained. Innovative Mexican methods used to produce loose (whole) cultured pearls from the indigenous rainbow-lipped pearl oyster (Pteria sterna) are described, together with the unique features of the pearls cultured in this bivalve.

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STAR GARNETS FROM ILAKAKA, MADAGASCAR

Dr. K. Schmetzer¹, Dr. H.-J. Bernhardt²
1. Petershausen, Germany
2. Central Microprobe Facility, Ruhr University, Bochum, Germany

ABSTRACT
Mineralogical and gemmological properties of six- and/or four-rayed star garnets from Ilakaka, Madagascar, are given. All three samples examined are intermediate members of the pyrope-almandine series. Asterism is caused by a dense network of inclusions that are oriented paralll to the two-fold axes or parallel to the three-fold axes of the cubic garnet hosts. The formation of different six- and/or four-rayed stars is discussed.

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THE SPRINGSURE DEPOSIT OF PRECIOUS OPAL

Roy Beattie
Brisbane, Queensland

ABSTRACT
The historic deposit of opal at Springsure, in central Queensland, was one of the early discovered deposits of precious opal in Queensland, and indeed in Australia. This discovery was made in 1872. Springsure opal, which occurs both in rhyolite and basalt, is a volcanic opal that displays features common to other deposits of volcanic opal worldwide. Unfortunately the Springsure deposit of precious opal has little economic significance, as its opal tends to 'crack', after mining and on exposure to ambient atmospheric conditions.

  T. Linton, K. Frazer
G.A.A. Instrument Evaluation Committee

ABSTRACT
Computer based programs for the identification and valuation (appraisal) of gemstones and gemstone-set jewellery are in a comparatively early stage of their development. The Gemchecker Professional (Pro) is a computerised system for management of gemstones and gemstone-set jewellery from the identification of their components to the assignment of value, and also stock control. Quality of information presented to the clients of valuers is one important aspect the jeweller-valuer or the gemmologist-valuer must carefully consider when an item of jewellery that may be set with gemstones is submitted for valuation. Clients do appreciate a clear, unambiguous presentation of the facts covering a valuation, even though they may have little appreciation of the complexities involved in the valuation process. The Gemchecker Pro does provide a modular system to facilitate valuations. As such, it is capable of performing many useful services for valuers of gemstones and gemstone-set jewellery.

One advantage the Gemchecker Pro system has is that its modular components are flexible, both in purchase and application. Importantly, the valuer who purchases this system only needs to purchase those modules necessary to perform the particular functions required for his or her individual business operation. Once the modules are chosen, their function and operation is controlled by simple- to-operate pull down boxes that allow rapid selection of chosen functions. 

  M.D.P.L.Francis¹, P.C.R. Dharmaratne²
1 Department of Earth Resources Engineering, University of Moratuwa, Sri Lanka
2 National Gem and Jewellery Authority, Colombo, Sri Lanka

ABSTRACT
Many source rocks for gemstones in Sri Lanka are related to carbonate rocks. Recent field investigations have revealed some unique reaction textures amongst corundum and spinel within such rocks. These finds indicate sequential reactions during corundum and spinel formation. One reaction is balanced, where corundum and phlogopite react to produce rims of spinel and K-feldspar around the corundum. Another reaction involves corundum and spinel replacement, but the reaction is unbalanced and needs more detailed analyses of the phases for its specification.