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Montana hosts the largest sapphire deposits in the US, but the genesis of and connection among the various secondary and primary sapphire occurrences remains cryptic. In situ SIMS measurements of oxygen isotopes in sapphires and zircon inclusions in sapphires provide an opportunity to study the isotope and trace element geochemistry in order to understand sapphire-forming protoliths (i.e. crustal setting and alteration). Sapphire from Montana was transported as xenocrysts in carrier (host) magmas that resorbed sapphire exteriors during transport. The timing and nature of sapphire genesis is elucidated by SIMS measurements of trace elements and U–Pb from discrete zones in zircon inclusions with rims that are interpreted to be syngenetic with host sapphire. Montana sapphires exhibit a large range of δ18O values, from −3‰ to +12‰ VSMOW. However, all but two anomalous crystals fall in the range of 0‰ to 8‰. There is significant crystal-to-crystal variability yet averages at most deposits are consistent with high-temperature equilibration with the mantle (δ18O(Crn) = 4.4‰ to 5.7‰), with the exception of the commercial sapphire deposits at Rock Creek that average 2.7‰. Ruby analyses are limited, but typically have lower δ18O values compared to sapphires from the same detrital localities. Homogeneity within individual crystals (avg. 2 s = ±0.2‰) indicates the absence of isotopically distinct fluid or melt during crystallization. But intercrystalline δ18O ranges by up to 7‰ at a single locality, suggesting sapphire variability at a deposit reflects heterogeneity in the original protolith. Oxygen isotope fractionations between zircon rims and surrounding sapphire suggest comagmatic zircon inclusions and corundum equilibrated at high temperature. No correlation is seen for the degree of radiation damage and alteration of δ18O(Zrc) when zircon inclusions are surrounded and armored by sapphire. U–Pb ages and trace elements were measured in a small subset of syngenetic zircon inclusions in Dry Cottonwood Creek sapphires, revealing a Proterozoic (1778 ± 9 Ma) age for the protolith of sapphires at this locality and a likely polygenetic history. Previous work has suggested formation of these sapphires through partial melting of anorthosites and several anorthosites occur locally and match the age of zircon inclusion cores—the Boehls Butte anorthosite (~180 km NW of Rock Creek) and the Bitterroot anorthosite (~55 km W of Rock Creek) could correlate with Al-rich protoliths at depth. Proterozoic U–Pb ages of zircon from the Boehls Butte anorthosite (1787 ± 2 Ma) match well with the age of zircon inclusion cores in Dry Cottonwood Creek sapphires and suggest genesis in these or similar protoliths. Zircon rims with Tera-Wasserburg lower intercept ages of 110 ± 9 Ma are consistent with previous observations of a xenocrystic relationship to the ~50 Ma Eocene volcanic rocks. Corundum that formed over 50 Ma prior to being scavenged by Eocene magmas likely originated by the anatexis of Precambrian anorthosites and possibly other aluminum-rich rocks at depth. [ABSTRACT FROM AUTHOR]

The beryl-group mineral johnkoivulaite, Cs(Be2B)Mg2Si6O18, was compressed hydrostatically in a diamond-anvil cell up to 10.2 GPa. In situ Raman spectroscopy and X-ray crystallography revealed a P6/mcc-to-P 3 c1 (second-order) phase transition on isothermal compression at the critical transition pressure Pc = 4.13 ± 0.07 GPa. The elastic parameters determined for the volume elasticity of the two polymorphs correspond to a Birch-Murnaghan equation of state with K0 = 148 ± 2 GPa and K ′ = 0 for P < Pc and K0 = 75.5 ± 0.9 GPa with K ′ = 4 for P > Pc. The low-P polymorph shows anomalously linear compression behavior, as reported for several other beryl-derived framework structures. The high-P polymorph, which was found to follow a a ′ = a ⋅ 3 , c ′ = c superstructure according to P 3 c1, is almost twice as compressible as its low-P form. This is unique for any beryl-derived structure and can be attributed to the high degree of freedom for atomic displacements in the superstructure. The reduced symmetry can also be understood as the effect of the driving mechanism of the transformation. The extra-framework Cs channel components counteract any lateral deformation of the channels parallel to [0001] within the microporous framework and, similar to pezzottaite, are responsible for maintaining the trigonal/hexagonal lattice metrics. [ABSTRACT FROM AUTHOR]

Oregon sunstone is a unique feldspar gemstone that displays a wide range of colors and optical effects due to the presence of metallic copper inclusions of various sizes and shapes. Most striking are the distinct green and red colors caused by copper particles, sometimes with strong red to green pleochroism. Recent computation work suggests that copper particles can strongly absorb and/or scatter light depending on the relative orientations of the feldspar crystal, the copper particles, and the polarization of the incident light, resulting in dramatically different appearances of the same crystal when viewed (or cut) along different directions. Common optical properties of Oregon sunstone are described and explained in detail in this paper, based on the optical theories of metallic nanoparticles in anisotropic media. Notably, it was found that the red to green colors observed can only be explained by considering both selective absorption and scattering from copper particles. The absorption and extinction spectra of the copper inclusions in Oregon sunstone are measured for different crystal orientations and polarizations. The scattering effect of the copper particles is quantified by subtracting absorption from extinction, the result of which agrees closely with the computed optical properties of spheroidal copper nanoparticles. The orientation of the anisotropic copper particles relative to the optical indicatrix of the feldspar is described. The correlation between the copper concentration profile and the "watermelon" color zoning in some Oregon sunstones is examined and discussed, along with a comparison to the color zones in treated, copper-diffused feldspar. Further studies on the diffusion and dissolution mechanisms of copper in feldspar crystals are required to fully understand the geologic processes that create these special gemstones in nature, which may provide additional methods to differentiate between treated and untreated stones. [ABSTRACT FROM AUTHOR]

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 spinel) and alexandrite. Spinel and alexandrite are both capable of producing photoluminescence with a long lifetime: spinel between 9 and 23 microseconds and alexandrite from 25 to 53 microseconds. The photoluminescence lifetime and exponential parameters of the half-life demonstrated notable differences in the ranges of decay times between natural, heated, and lab-grown versions of these materials. [ABSTRACT FROM AUTHOR]

The article focuses on the second annual Turquoise United Conference 2023 held at the Albuquerque Convention Center, aiming to unite members of the turquoise industry for discussion and collaboration. Topics discussed include sessions on laws governing turquoise jewelry, the implementation of a turquoise grading system, and courses on turquoise basics and collecting, with highlights on a highest-grade turquoise stone contest and research presentation on the Mona Lisa mine.

The article offers information about gem inclusions as mineral crystals or cavities filled with fluid and/or gas that occur in a host gemstone. It mentions that inclusions are important for determining the natural, synthetic, or treated character of a gem, and for establishing the likely geographic origin of a valuable colored stone.

The article discusses the identification of an exceptionally rare titanoholtite, a dumortierite supergroup mineral, based on its distinct physical properties and chemistry, which deviate from typical dumortierite characteristics, challenging previous assumptions about its composition and rarity.

A new mineral of the beryl group, johnkoivulaite, Cs(Be2B)Mg2Si6O18, was recovered from the gem gravels in the Pein Pyit area of the Mogok region in Myanmar. Thus far, only a single crystal has been identified. It has dimensions of about 5.8 x 5.7 x 5.5 mm. This specimen has an irregular shape but still has discernible crystal form with geometric growth patterns observed on the crystal faces. The crystal of johnkoivulaite is grayish-violet in color and strongly pleochroic, going from nearly colorless with E⊥c to dark bluish-violet with E||c. Johnkoivulaite has a Mohs hardness of about 7 1/2 and a measured density of 3.01(10) g/cm³. It is uniaxial (-) with ω = 1.607(1) and ε = 1.605(1) (white light). Electron microprobe analyses gave the empirical formula of (Cs0.85K0.10Na0.01) (Be1.88B1.12) (Mg1.66Fe0.27 Mn0.01Al0.05) (Si5.98)O18 with Be calculated by stoichiometry and confirmed by LA-ICP-MS measurements. Johnkoivulaite is hexagonal, P6/mmc (no. 192) with a = 9.469(2), c = 9.033(2) Å, V = 701.5(3) ų, and Z = 2. Johnkoivulaite is isostructural with beryl and exhibits partial substitution of B for Be at the distorted tetrahedral site, Mg for Al at the octahedral site, and Cs in the channel sites within the stacked Si6O18 rings. This substitution can be written as (CsMg2B)(□Al2Be)-1. Johnkoivulaite, the seventh member of the beryl group, is named in honor of gemologist John Koivula in recognition of his contributions to mineralogy and gemology. [ABSTRACT FROM AUTHOR]

Color is the most important quality for colored stones, one that is widely discussed and studied by gemologists. Understanding the color characteristics of a gemstone can provide a scientific basis to guide its cutting. This study uses visible spectroscopy to determine the unpolarized spectra of a uniaxial material from the polarized spectra (o-ray and e-ray) in order to predict the color of a uniaxial gem material when viewed in any direction. A seemingly intuitive way of doing this, by adding weighted amounts of the o-ray and e-ray absorption spectra, does not actually work for estimating the unpolarized spectra. The mathematically and physically correct way to reconstruct these unpolarized spectra is to add weighted polarized transmittance spectra and then to convert back to absorption if desired. This method allows color to be accurately predicted for a material when viewed in any direction as long as the polarized spectra and the viewing angle relative to the c-axis are known. This method has been verified by comparison with a synthetic V-bearing sapphire and a synthetic Cr-bearing sapphire cut into wafers (not faceted gemstones) at various angles relative to the optic axis. [ABSTRACT FROM AUTHOR]

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 study the electrical properties of solution-grown Al-doped ZnO nanowires as a function of composition from 0 to 4 at. % Al:Zn. Carrier mobility and charge density extracted from sensitive optical absorption measurements are in agreement with those extracted from single-wire field-effect transistor devices. The mobility in undoped nanowires is 28 cm2/V s and decreases to ∼14 cm2/V s at the highest doping density, though the carrier density remains approximately constant (1020 cm-3) due to limited dopant activation or the creation of charge-compensating defects. Additionally, the local geometry of the Al dopant is studied by nuclear magnetic resonance, showing the occupation of a variety of dopant sites. [ABSTRACT FROM AUTHOR]

The gem and jewelry trade has come to place increasing importance on the geographic origin of alexandrite, as it can have a significant impact on value. Alexandrites from Russia and Brazil are usually more highly valued than those from other countries. In 2016, GIA began researching geographic origin of alexandrite with the intent of offering origin determination as a laboratory service. Unfortunately, collecting reliable samples with known provenance can be very difficult. Alexandrite is often recovered as a byproduct of mining for other gemstones (e.g., emerald and corundum), so it can be difficult to secure reliable parcels of samples because production is typically erratic and unpredictable. The reference materials studied here were examined thoroughly for their trace element chemistry profiles, characteristic color-change ranges under daylight-equivalent and incandescent illumination, and inclusion scenes. The data obtained so far allow us to accurately determine geographic origin for alexandrites from Russia, Brazil, Sri Lanka, Tanzania, and India. Future work may help to differentiate alexandrites from other localities. [ABSTRACT FROM AUTHOR]

The gem world is rich with species of tourmaline such as the vivid greens of dravite, uvite, chromium-dravite, and vanadium-dravite; the pinks of elbaite and rossmanite; and the multicolored fluor-liddicoatite. To date, simple gemological tests to separate these various species, and many others of the tourmaline group, are lacking. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) analysis is becoming a prevalent method to measure chemical composition in gemstones because it provides inexpensive, clean, fast, and largely nondestructive analyses. With adequate standards and calibration, this technique can quantitatively measure six common major elements in tourmaline (Na, Ca, Mg, Fe, Al, and Si) as well as trace elements (Cr, V). These data provide the basis for a simplified classification of gem tourmalines. Analyses of 14 tourmalines by both electron probe microanalysis (EPMA) and LA-ICP-MS for major and minor elements demonstrates that an LA-ICP-MS system with proper calibration, standardization, and normalization is capable of accurate measurements of six major elements in tourmalines, generally within ±10% error. While some volatile elements such as H, Li, B, and F cannot be measured reliably by this technique, a data reduction scheme can be implemented to calculate those elements based on select assumptions of concentrations of other major elements. Thus, LA-ICP-MS analysis is ideal for some tourmaline species determination in a gemological laboratory setting. The ability to provide a simple tourmaline species classification will enhance GIA identification reports and provide additional tools for identification. [ABSTRACT FROM AUTHOR]

The article discusses a unique partially non-nacreous blister pearl obtained from Pinctada radiata in Bahrain, detailing its unusual characteristics and scientific examination. Topics include the pearl's physical attributes, structural features, and reactions under various tests, shedding light on its formation and significance in gemological research.