New gemstone occurrences in the south-west of Madagascar

Milisenda, Claudio C.; Henn, Ulrich; Henn, Jürgen

doi:10.15506/jog.2001.27.7.385

Cited by 13 publications

(9 citation statements)

References 13 publications

(35 reference statements)

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“…Alexandrite originating from phlogopite-bearing host rocks comes from primary emerald deposits in the Mananjary region of Madagascar (Schmetzer and Malsy, 2011a). The other deposit, in the Ilakaka region (Hänni, 1999;Milisenda et al, 2001), is a secondary deposit where different varieties of chrysoberyl-including alexandrite-have been found. Occasionally, large alexandrite crystals of gem quality have been recovered in the Lake Alaotra region.…”

Section: Alexandrite Geographic Localities: a Brief Summarymentioning

confidence: 99%

Geographic Origin Determination of Alexandrite

Sun¹,

Palke²,

Muyal³

et al. 2019

G&G

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A fter the discovery of a gem mineral with unusual color-change behavior in the Russian Ural Mountains during the early 1830s, Swedish mineralogist Nils Adolf Erik Nordenskiöld named this new gem alexandrite in 1834 in honor of the future Czar Alexander II (Kozlov, 2005). This immediately created a royal and romantic aura around this variety of chrysoberyl. The most coveted alexandrites exhibit a lush green to greenish blue color in daylight and a warm, bright red shade in candlelight (Levine, 2008); some fine Brazilian and Indian alexandrite examples are shown in figures 1-3 and 6. This phenomenal color change is caused by the presence of trace Cr 3+ substituting for Al 3+ in the chrysoberyl crystal structure. Alexandrite is routinely described as "emerald by day, ruby by night." It is a stone of duality-green or red, cool or warm, day or night (Levine, 2008). Because of its rare and attractive color-change phenomenon, alexandrite has been highly sought after and is one of the most valuable gemstones in the trade. Alexandrite, particularly fine-quality material, is also very scarce; it has generally been a byproduct of mining other major colored stones. Overall production statistics are hard to evaluate. It has been mined

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Section: Alexandrite Geographic Localities: a Brief Summarymentioning

confidence: 99%

Geographic Origin Determination of Alexandrite

Sun¹,

Palke²,

Muyal³

et al. 2019

G&G

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show abstract

“…In the cutting and sorting processes in Thailand, material from Tunduru is commonly mixed with imported rough from Ilakaka, Madagascar. However, at the time of writing (March 2007) gems of the taaffeite group have neither been reported from Ilakaka (see, for example, Schmetzer, 2000;Milisenda et al, 2001) nor identified in the laboratory of the Institut de Gemmologie de Madagascar in Antananarivo (T. Ramerison, pers. comm., 2006).…”

Section: Methodsmentioning

confidence: 99%

A description of pearl farming with Pinctada maxima in South East Asia

Hänni¹

2007

Journ of Gemm

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This reports on a modern pearl farm in South East Asia which uses Pinctada maxima oysters. Marine biologists and geneticists supervise the pearling process. Culturing oysters from fertilized eggs has generally replaced wild oyster collection. In hatcheries larvae and spat are reared under scientifically controlled conditions. After around two years the oysters are about 12 cm in size and ready for the operation. Careful selection of donor oysters for the tissue graft and of host oysters to grow the pearls ensures optimum conditions for pearl formation. Excellent environmental conditions are sought to grow pearls of superior quality. High standards of working hygiene, X-ray checks and regular and frequent cleaning of the oysters and the holding nets are further steps to ensure high quality. Almost four years from the hatching of the larvae, the oysters are ready for a first pearl harvest. Most of the oysters are not re-beaded, and their muscle flesh is processed as seafood and the shells utilized for their nacre. The pearls are graded for quality and marketed mainly in Australia.

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“…UV-Vis-NIR absorption spectra of all samples were similar to other magmatic-related origin sapphires. The examination revealed Fe 3+ -related peak at 380-390 nm and 450 nm, [3,15,16] while absorption band due to Fe 2+ −Ti 4+ IVCT displayed between 500 and 800 nm [9,[15][16][17][18] and strong broad absorption band toward the near-infrared region, which thought to be related to Fe 2+ −Fe 3+ IVCT, [3,9] possibly with the involvement of Fe 2+ -Fe 3+ -Ti 4+ clusters. [7,15,[19][20][21] However, Na-Phattalung et al(2018) [8] proposed that the absorption of Fe 2+ −Ti 4+ IVCT from the simulation should present at 623 and 912 nm, which the former was not apparent in this study and the latter could be superimposed by the strong broad absorption band toward near-infrared region (Fig-…”

Section: Uv-vis-nir Absorption Spectroscopymentioning

confidence: 99%

Investigation of Blue Coloration in Sapphires Using X‐Ray Absorption Near‐Edge Structure Spectroscopy (XANES)

Amphon

Chankhantha

Thammajak³

et al. 2022

Cryst. Res. Technol.

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The color of blue sapphire has long been explained using the intervalence charge‐transfer (IVCT) [Fe2+‐Ti4+ and/or Fe2+‐Fe3+] theory, in which the blue can be reduced by thermal (heat) treatment in oxidizing condition to alter Fe2+ (FeO) to Fe3+ (Fe2O3). However, the color mechanism is not well understood. Recently, the band gap theory proposes that iron (Fe) in sapphire always presents as Fe3+, and the blue is caused by Fe3+‐Ti4+ pair, hence thermal treatment does not alter Fe oxidation. The UV–Vis–NIR, Proton‐Induced X‐ray Emission (PIXE), and X‐ray Absorption Near‐Edge Structure (XANES) techniques are carried out before and after treatment to prove this issue. The absorption spectra are slightly lower after treatment, corresponding with the reduction of blue color in all samples. XANES data reveal mixture of Fe2+ and Fe3+ (mainly Fe3+) in all samples, and show insignificantly change after heated which rather supports the band gap theory. However, calculation based on linear combination fitting (LCF) technique shows a slight change in the oxidation from Fe2+ to Fe3+ which rather supports the IVCT theory. It is noted that the highest change is found in the lowest ratio of Fe:Ti sample, while the lowest change is conversely.

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New gemstone occurrences in the south-west of Madagascar

Cited by 13 publications

References 13 publications

Geographic Origin Determination of Alexandrite

Geographic Origin Determination of Alexandrite

A description of pearl farming with Pinctada maxima in South East Asia

Investigation of Blue Coloration in Sapphires Using X‐Ray Absorption Near‐Edge Structure Spectroscopy (XANES)

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