Aaron Palke

Gemological Institute of America

Research on photoluminescence spectroscopy on Cr-doped gem materials has demonstrated great success regarding the identification of gemstones in terms of building rapid test systems. In this study, 405 nm photoluminescence spectroscopy was used to measure the luminescence decay profiles of dozens of natural and lab-grown spinel (including heated sp...

https://www.gia.edu/gia-news-research/nickel-diffused-spinel

The optical properties (scattering, absorption and extinction) of spheroidal Cu particles embedded in intermediate plagioclase feldspar are computed for various sizes and shapes using the Mie theory and T-matrix method. The observed color for Cu-bearing plagioclase, as a function of particle size and shape, is also calculated from the computed exti...

Iron oxide inclusions and exsolution lamellae in rainbow lattice sunstone (RLS) from Harts Range, Australia, are examined using optical and electron microscopy and single-crystal X-ray diffraction (SC-XRD). Laser ablation inductively coupled plasma mass spectrometer (LA-ICP-MS) analyses show a bulk composition of An1.4Ab14.8Or83.0Cn0.8 with < 200 p...

The color of most garnets is derived from multiple color‐producing elements (chromophores). In this study we selectively isolate the ultraviolet–visible–near infrared (UV–Vis–NIR) spectra of four major chromophores (Fe ²⁺ , Mn ²⁺ , Cr ³⁺ and V ³⁺ ) by collecting and extrapolating the spectra of four representative pyrope‐almandine‐spessartine (pyra...

This study compares two purple gem spinel samples with regard to trace element chemistry and visible light absorption spectra, and presents the first reported example of a spinel with a saturated purple color caused predominantly by chromium and cobalt. Sample VN, from a placer deposit in the Luc Yen district of Vietnam, exhibited strong saturation...

A new mineral of the beryl group, johnkoivulaite, Cs(Be2B)Mg2Si6O18, was recovered from the gem gravels of the Pein Pyit area of the Mogok region in Myanmar. Thus far, only a single crystal has been identified. It has dimensions about 5.8×5.7×5.5 mm. This specimen has an irregular shape but still has discernible crystal form with geometric growth p...

Raman and photoluminescence (PL) mapping is a non-destructive method which allows gemologists and scientists to evaluate the spatial distributions of defects within a gem; it can also provide a method to quickly distinguish different species within a composite gem. This article provides a summary of this relatively new technology and its instrument...

The red variety of corundum owes its color and strong fluorescence to the presence of Cr, as well as traces of Fe. The latter can reduce the fluorescence and thus impact the appearance of the final gem. Gem quality rubies are rarely available for scientific study and even less common in their rough form. Opaque inclusions in rubies are often remove...

Gem corundum deposits are typically divided into blue sapphire and ruby deposits. However, this classification often overlooks the fact that the precious stones produced are the same mineral with only an overall slight difference in their trace element profiles. It can take only a couple thousand ppm chromium to create the rich, red color expected...

Ethiopia, traditionally known for opal, has become an important source for emerald and sapphire. After these significant discoveries, a new type of Cu-bearing sunstone feldspar, first shown in 2015 to Tewodros Sintayehu (Orbit Ethiopia Plc.), was discovered in the Afar region (L. Kiefert et al., “Sunstone labradorite-bytownite from Ethiopia,” Journ...

A new mineral, johnkoivulaite, has been named in honor of John Koivula, a renowned microscopist and preeminent researcher at GIA for more than 40 years. In collaboration with scientists from the California Institute of Technology, Dr. Kyaw Thu of Macle Gem Trade Laboratory, and Nay Myo, a gem dealer from Mogok, GIA researchers described johnkoivula...

Yogo Gulch in central Montana is one of the most important gem deposits in the United States. Although very little material has been recovered there in recent years, it has produced several million carats of rough sapphire over the course of its history (Voynick, 2001). These stones, known for their vibrant untreated blue color and high clarity, ha...

In studies of the structures of silicate minerals and glasses, 29Si NMR spectroscopy has been applied almost exclusively to materials containing relatively low concentrations of ions with unpaired electrons spins, such as most transition metals and rare earths, because of sometimes severe broadening and shifting of resonances in such strongly param...

A wide number of genetic models have been proposed for volcanically transported ruby and sapphire deposits around the world. In this contribution we compare the trace element chemistry, mineral and melt inclusions, and oxygen isotope ratios in blue to reddish-violet sapphires from Yogo Gulch, Montana, U.S.A., with rubies from the Chantaburi-Trat re...

Pleochroism plays an important role in determining the face-up visual color appearance of faceted, optically anisotropic (non-cubic) gemstones. One area that has received little attention is the interplay between pleochroism and the so-called alexandrite effect wherein the perceived color of a mineral changes with different lighting conditions (i.e...

Trace-element chemistry and microscopic observations of included gem corundum (α-Al2O3) suggests a new model of syngenetic growth of oriented rutile inclusions rather than the usual interpretation of their growth through exsolution. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is now a robust method for measuring trace el...

Most applications of high-resolution NMR to questions of short-range order/disorder in inorganic materials have been made in systems where ions with unpaired electron spins are of negligible concentration, with structural information extracted primarily from chemical shifts, quadrupolar coupling parameters, and nuclear dipolar couplings. In some ca...

We report here compositions of glassy melt inclusions hosted in sapphires (gem quality corundum) from three alluvial deposits in Montana, USA including the Rock Creek, Dry Cottonwood Creek, and Missouri River deposits. While it is likely that sapphires in these deposits were transported to the surface by Eocene age volcanic events, their ultimate o...

Gem corundum (sapphire) has been mined from an ultramafic lamprophyre dike at Yogo Gulch in central Montana for over 100 years. The sapphires bear signs of corrosion showing that they were not in equilibrium with the lamprophyre that transported them; however, their genesis is poorly understood. We report here the observation of minute glassy melt...

Pyrope-rich garnet is an important "sink" for trivalent transition metals such as Cr^3+, V^3+, and Fe^3+ in Earth's upper mantle. In order to obtain a better crystal-chemical understanding of transition metals in garnet and especially pyrope solid solutions, 27^Al and 29^Si MAS NMR spectra were collected on synthetic crystals of composition Mg3(Al0...

A type of pink pyrope garnet containing vanadium and chromium, believed to have been mined in Tanzania, appeared at the 2015 Tucson shows. The material shows a noticeable color difference from purplish pink under incandescent light (A) to purple under daylightequivalent light (D65). This study reports a quantitative analysis of the difference in co...

Cation Order-Disorder Behavior in Silicate Garnet Solid Solutions Most rock-forming silicates are substitutional solid solutions and extensive research has been done to determine their cation order-disorder behavior. In the case of aluminosilicate garnet (X3Al2Si3O12 with X = Mg, Fe^2+, Mn^2+ and Ca) both synthetic and natural solid-solution cryst...

An attempt is made for the first time to measure the local (short-range) distribution of the X-cations in a ternary almandinepyrope-grossular garnet solid solution using paramagnetically shifted NMR resonances. Initial 27Al MAS NMR measurements made on an almandine-rich garnet of composition Alm45Prp42Grs13 proved to be uninterpretable because of t...

The Local Structural State of a Kimberlitic Grospydite Garnet using Paramagnetically Shifted 27^Al and 29^Si MAS NMR Resonances C.A. Geiger1, A.C. Palke2, and J.F. Stebbins2 1Materials Science and Physics, Salzburg University, Hellbrunnerstrasse 34, A-5020 Salzburg, Austria 2Geological and Environmental Sciences, Stanford University, Stanford, C...

In marked contrast to the single, narrow 29Si MAS NMR resonance for pure forsterite (Mg2SiO4), the spectra for synthetic forsterite containing 0.05 to 5% of the Mg2+ replaced with Ni2+, Co2+, or Fe2+ display between 4 and 26 additional, small, paramagnetically shifted peaks that are caused by interactions of the unpaired electron spins on the trans...

A suite of Fe-bearing natural and synthetic grossular-rich [(Ca,Fe)3(Al,Fe)2Si3O12] and pyrope-rich [(Mg,Fe)3Al2Si3O12] garnets were investigated using 27^Al and 29^Si MAS NMR and 57^Fe Mössbauer spectroscopy. This was done to study the state of cation order-disorder in garnet solid solutions by analyzing paramagnetically shifted resonances in high...

Most rock-forming silicates are substitutional solid solutions. The distribution of their cations affects a number of properties such as thermodynamic behavior. For aluminosilicate garnet solid solutions (X3Al2Si3O12 with X = Mg, Fe^2+, Mn^2+ and Ca) crystals have random long-range X-cation disorder in space group Ia-3d. It is assumed, as with most...

We present (31)P magic angle spinning nuclear magnetic resonance spectra of flux-grown solid solutions of La1-xCexPO4 (x between 0.027 and 0.32) having the monoclinic monazite structure, and of Y1-xMxPO4 (M = V(n+), Ce(3+), Nd(3+), x between 0.001 and 0.014) having the tetragonal zircon structure. Paramagnetically shifted NMR resonances are observe...

We present 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra of Al- and Fe-bearing, high-pressure pyroxene and perovskite samples, synthesized in a multi-anvil apparatus at 26 GPa and 1900 °C at targeted compositions of (Mg1−xFex)(Si1−xAlx)O3 (x = 0.01, 0.025, and 0.05). 27Al MAS-NMR spectra of the perovskite samples i...

The boundary between the Earth's upper and lower mantle is generally attributed to the decomposition of (Mg,Fe)2SiO4 ringwoodite into ferropericlase and perovskite-structured (Mg,Fe)SiO3, hereafter perovskite. Concomitant with this phase change is the more gradual disappearance of a separate Al-bearing phase (majoritic garnet) and dissolution of Al...

We present the results of a variable-temperature (VT) 31P magic angle spinning NMR (MAS-NMR) study of a series of solid solutions between different synthetic rare earth (RE = Y, La, Ce, Pr, Nd, Eu, Dy) orthophosphates (REPO4) taking either the monoclinic monazite or tetragonal xenotime (zircon) crystal structure. Solid solutions were formed by mixi...

We present variable-temperature (VT, 31 to 204 °C) 29Si magic angle spinning NMR (MAS-NMR) spectra of a synthetic forsterite containing dilute paramagnetic impurities and 27Al and 29Si spectra of two iron-bearing natural pyrope garnet specimens from the Dora Maira ultrahigh-pressure metamorphism locality. Previous NMR studies of these materials rep...

The analysis of transparent conducting oxide nanostructures suffers from a lack of high throughput yet quantitatively sensitive set of analytical techniques that can properly assess their electrical properties and serve both as characterization and diagnosis tools. This is addressed by applying a comprehensive set of characterization techniques to...

Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) has long been used to obtain structural information of geologically important minerals and glasses. The presence of paramagnetic ions such as Fe2+, Fe3+, Co2+, Ni2+, and rare earth elements may lead to ``paramagnetically-shifted'' NMR peaks. Previous work on 27Al and 29Si NMR on natural pyro...

The use of ZnO nanowires has become a widespread topic of interest in optoelectronics. In order to correctly assess the quality, functionality, and possible applications of such nanostructures it is important to accurately understand their electrical and optical properties. Aluminum- and gallium-doped crystalline ZnO nanowires were synthesized usin...

The 2005-2006 eruption along a well-surveyed part of the East Pacific Rise (EPR) at 9°50"N, and the subsequent observations and collection of the flow (Soule et al., 2007) provide a rare opportunity to study how submarine basalts vesiculate as they ascend beneath the mid-ocean ridge (MOR) and are emplaced at the surface. We have measured dissolved...

Lake Tanganyika is the oldest and largest of the East African rift lakes and vital to the economy of the surrounding villages and countries. Deforestation around the lake causes many negative effects from an increased sediment flux and has changed dramatically as a function of population. Increases in inorganic sediment flux from deforested watersh...

When lavas ascend and erupt along mid-ocean ridges, they are usually oversaturated with dissolved volatiles (especially CO2) because of the pressure dependence of volatile solubility. If the lava is not quenched to glass immediately after eruption, CO2 may exsolve into vesicles and/or be lost into seawater. This process is time dependent and could...