Franck Notari

GGTL Laboratories Switzerland

This study covers hydrogen-rich fancy color diamonds that exhibit complex spectra from the UV all the way to the mid-IR. The diamonds with such spectra that are included here show a large range of colors from brownish yellow to brown, yellow-green to olive and gray to violet. The color origin of such diamonds has always been stated as “hydrogen-rel...

While the first part of this study took a detailed look at the properties, defects and classification of brown diamonds with deformation-related (DR) brown color and compared them to pink to purple to red diamonds, this second part covers diamonds with non-deformation-related (referred to as NDR in this study) brown color, including diamonds with t...

For this study, the properties of a large sample of various types of brown diamonds with a deformation-related (referred to as “DR” in this work) color were studied to properly characterize and classify such diamonds, and to compare them to pink to purple to red diamonds. The acquisition of low temperature NIR spectra for a large range of brown dia...

We document a dichromatism effect in gem andalusite that shifts from light brownish pink at low thickness to medium green at high thickness. This is roughly reverse to that usually observed in other dichromatic materials. We show that this is due to a very strong pleochroism in andalusite, when dichromatism in other materials is due to an alexandri...

Treated green diamonds can show residual radioactivity, generally due to immersion in radium salts. We report various activity measurements on two radioactive diamonds. The activity was characterized by alpha and gamma ray spectrometry, and the radon emanation was measured by alpha counting of a frozen source. Even when no residual radium contamina...

During the March 2015 Diamond Show in Basel, Switzerland, a parcel of 6,000 melee-sized colourless diamonds was analysed using the GGTL Diamond Fluorescence Imaging (DFI) Laser+ fluorescence imaging and spectroscopy system. From the entire parcel, one sample stood out clearly with unusual fluorescence colours and distribution, combined with a photo...

The physical and optical properties of an exceptional asteriated diamond called The Rhodesian Star are described in detail. The stone shows a dramatic six-lobed star pattern formed by a dark grey cloud that strongly contrasts with the diamond's light greenish grey-yellow body colour. Analysis by various optical and spectroscopic methods identified...

The properties of 152 natural diamonds with C centers – detectable by the absorptions at about 1344 and/or 2688 cm−1 in the infrared spectra – were analyzed in order to better understand their origin of color. While such diamonds are generally thought to be yellow, type Ib natural diamonds are usually not so, but mainly orange-yellow, orange, brown...

The methods of luminescence spectroscopy and microscopy are widely used for the analysis of gem materials. This paper gives an overview of the most important applications of the analysis of laser and UV excited luminescence by spectroscopy and visually by microscopy with emphasis on diamond, and specifically natural type Ib diamond, little studied...

Seventy-six diamonds with detectable C centers were selected based on the presence of a 1344 and/or 2688 cm–1 absorption in their infrared (IR) spectra. Such diamonds are always distinctly colored, often in yellow to orange with various modifications of colours such as brown and green. Fifty-seven of them had an IR spectrum exhibiting the well-know...

The infrared spectra of 68 natural and synthetic diamonds with detectable C centers at about 1130 cm− 1 and 1344 cm− 1 were recorded. After correction and normalization of the spectra there was an attempt to determine the A, B and C center nitrogen content of the samples using the spectral fitting spreadsheet supplied by David Fisher from the DTC....

The infrared spectra of 68 natural and synthetic diamonds with detectable C centers at about 1130 cm−1 and 1344 cm−1 were recorded. After correction and normalization of the spectra there was an attempt to determine the A, B and C center nitrogen content of the samples using the spectral fitting spreadsheet supplied by David Fisher from the DTC. It...

A 0.23 g orangy brown crystal, a 0.39 ct step-cut gem later faceted from it, and a 0.71 g crystal-all reportedly from Myanmar-were characterized for this report. Infrared spectroscopy, X-ray diffraction, and chemical analysis identified the material as hibonite. These samples represent the first gem-quality hibonite ever recorded.

Neutron- and electron-irradiated type Ia “black” diamonds were analyzed: three near colorless type Ia diamonds were treated in a nuclear reactor with a dose of 1.8 × 1017 neutrons/cm2 and three equivalent samples were irradiated in an electron accelerator with a dose of approximately 0.5 GGy 10 MeV electrons. The diamonds were then annealed and ana...

Identifying faceted gemstones involves practices that are closely related to the classical determinative methods used by mineralogists. Measurements of optical and physical properties, combined with acute observation using various illumination techniques, are usually sufficient to determine the nature of a gem. Determining the geographic origin of...

Three natural, treated-color diamonds present photoinduced H1b/H1c centers after UV exposure. As the H1b/H1c absorptions increase, that of the 595 nm center decreases. Recovery occurs by simple exposure to a standard incandescent 100 W lamp. The centers implied are all related to nitrogen and to the existence of a treatment, the formation of H1b/H1...

Ten type I diamonds containing CO2 and three diamonds related to these (referred to as “Pseudo CO2” diamonds) were treated by the HPHT process to observe changes in colour, colour distribution, inclusions, luminescence and spectral features in the visible to the mid-infrared regions. All samples were of predominantly brown colour before the treatme...

Well-formed crystals of green tourmaline from northwestern Zambia show a growth pattern reminiscent of trapiche emerald/ruby when sliced perpendicular to the c-axis. In fact, such slices were originally encountered in parcels sold as emerald in Zambia. The trapiche appearance most likely originates from skeletal growth, with the pattern formed by a...

"Rainbow" andradite from Nara, Japan, occurs as relatively small orangy brown crystals that show attractive iridescence in almost the entire range of the spectrum. The material is nearly pure andradite, as determined by its chemical composition and Vis-NIR and specular reflectance FTIR spectra. Microscopy revealed that two different types of lamell...

Unusual brown to yellow diamonds of mixed type Ib/IaAB were analyzed. The occurrence of nitrogen in a combination of A, B and C centers directly detectable by IR spectroscopy in natural diamonds is considered to be extremely rare. We propose to call such stones ABC diamonds for short. These diamonds are characterized by a color, luminescence, and a...

We describe here diamonds with planar segments of limited lateral extension, some of which have dissolved to form flat etch channels. We have documented such features only in diamonds which show otherwise lamellae of brown or pink color due to plastic deformation along (111) planes, called “colored graining lamellae”. The planar segments are identi...

The amber centres are a series of similar near-infrared absorptions found in brown “amber”-coloured diamonds. These centres are found exclusively in crystals showing lamellae of plastic deformation (“brown graining”) and nitrogen in the form of A-aggregates, at least. They represent likely electronic transitions responsible for up to six zero-phono...

Three historical ‘asteriated’ diamond slices present mixed-habit growth with contemporaneous lobe-shaped cuboid sectors and octahedral sectors. The lobe shape is explained by continuous variation of the relative growth rates. Nitrogen concentration in octahedral sectors is higher than in cuboid sectors, whereas hydrogen is incorporated mostly in cu...