corundum, inclusions.5, Montana.12, USA.12, gems

Two-phase inclusions are common in many sapphires. Physical and chemical analysis of the gas and liquid phases present in these inclusions can shed light on the formation conditions of alluvial sapphires, even in the absence of evidence of source rock lithology. We report here some initial observations of a different type of two-phase inclusion, seen in alluvial sapphires from the Rock Creek and Missouri River deposits in the state of Montana. At first glance, these inclusions appeared to be ordinary gas-liquid inclusions (left image); however, polishing through the inclusions demonstrated that the “liquid” component was actually a glassy solid. The identification of the solid as a glass rested with the phase’s optically isotropic nature and the lack of an identifiable Raman spectroscopic signal attributable to any crystalline phase. Glassy melt inclusions in Montana sapphires were previously documented by John Koivula (R.W. Hughes, Ruby & Sapphire, RWH Publishing, Boulder, Colorado, 2007, pp. 468–469). Electron microprobe analysis (EPMA) of glass inclusions from several samples showed them to be dacitic to trachydacitic in composition. In this sense the inclusions are ordinary two-phase inclusions in which the original liquid phase was a silicic magma that quenched to form a silicate glass. The gas phase is presumed to have originally been dissolved in the silicate magma. Later exsolution produced a separate gas phase as volatile solubility in the magma decreased due to falling pressure and/or temperature. Volatile exsolution likely also led to the discoid fractures commonly seen around melt inclusions, which are filled with silicate liquid and/or the volatiles themselves (again, see left image). The center image captures a snapshot of the process of volatile exsolution and the “bursting” of the two-phase inclusions, in which multiple gas bubbles seem to have precipitated instantaneously as the inclusion exploded out into the surrounding corundum. Due to the high relief of the silicate glass, these discoid fractures often have a “flux”-like appearance. In some cases, the fractures seem to have partially healed, leaving hexagonal geometric patterns as evidence of the crystallographic orientation of the sapphire host (right image). Further work is being carried out to characterize these inclusions and to decipher the story they have to tell about the genesis of alluvial Montana sapphires.

corundum, treatments.6, oiling in ruby, gems

Reports the examination of a 12.12 ct natural ruby whose inclusions and chemical composition were consistent with Myanmar origin, with no evidence of heat treatment. Microscopy revealed material within surface-reaching fractures, including flattened bubbles, whitish residues and patterns resembling dried oil in treated emeralds. Droplets formed at fracture openings under the warmth of fibre-optic illumination, while DiamondView imaging highlighted the filling’s luminescence. Infrared absorption confirmed an organic substance, with bands supporting identification as oil. The authors concluded that the ruby showed moderate transparency enhancement by fracture filling, probably with oil, documenting an unusual treatment in a large Myanmar ruby.

gems, beryl, emerald, Afghanistan, Brazil, Colombia, Zambia, Zimbabwe, inclusions

corundum, inclusions.5, Madagascar.12, gems

The age determination of zircon inclusions in faceted sapphires by LA-ICP-MS may provide a valuable tool to support geographical origin determination. In this initial study, U–Pb dating of a zircon inclusion in a pink sapphire from Madagascar yielded an age of 650 million years (Ma), suggesting a syngenetic origin (i.e., formed at the same time as the host sapphire) of the zircon. In a greenish blue sapphire from Madagascar, an included zircon yielded a U–Pb age of 1,750 Ma, pre-dating the host sapphire, and therefore indicating the zircon is an inherited inclusion (i.e., it originated from rocks that existed before the host sapphire crystallized). These results are supported by indications provided from conventional methods of geographical origin determination. This article also discusses the potential influence on U–Pb age dating of post-formation metamorphic events, laboratory heat treatment, and the possibility of complex zoning in the zircon inclusions.

gems, Brazil, Emerald, Piteiras, fluid inclusions, gemology, provenance, microthermometry

New fluid inclusion analyses—using a range of techniques including quadrupole mass spectrometry coupled with gemmological investigations—were conducted on rough and gem-quality faceted emeralds from the Piteiras Mine, Minas Gerais, Brazil. These data complement those of Rondeau et al. (2003), who also studied emeralds from this locality. The emeralds typically occur as euhedral to anhedral crystals disseminated in biotite-phlogopite schist and range from 0.5 to 50 mm in length. Mineralization is closely associated with alkaline metasomatized pegmatite bodies, quartz boudins and veins, and talc-chlorite bands. Four types of fluid inclusions have been identified, including aqueous brine and aqueous carbonic inclusions containing one or two liquid phases, gas bubbles, and/or solid crystals such as carbonates. Primary fluid inclusions in the emeralds record salinities of approximately 4–24 equivalent wt.% NaCl and minimum trapping temperatures ranging from ~350 to 480 °C. Combined microthermometry, Raman spectroscopy, and crush-leach gas analyses reveal that the mineralizing fluid was an aqueous carbonic brine enriched in reduced volatile species such as CH₄, N₂, H₂S, and alkanes. In terms of optical properties (RI ε = 1.573–1.580; RI ω = 1.580–1.588; birefringence = 0.006–0.008) and specific gravity (2.65–2.78), the Piteiras emeralds fall within the expected range for metasomatic, schist-hosted emeralds.

gems, jade, amphibole jade, nephrite, China

The Yurungkax river and Karakax River ( White Jade and Black Jade) are two main placer nephrite sites located in Hetian, Xinjiang. They are well known historically for their valuable white, green and black nephrite, respectively, with a long history of use in the world. In this study, electron microprobe ( EPMA) analysis was used to study green nephrite samples. The result shows that low Cr and Ni ( Cr2 O3 = 0. 00 to 0. 06% and NiO = 0. 00 to 0. 09%, respectively) are constant in these samples, consistent with the content of the marble type nephrite but different from the content of serpentinite related nephrite ( Cr2 O3 = 0. 07% to 0. 43% and NiO = 0. 08% to 0. 36% ). The accessory minerals in green nephrite include zircon, rutile, titanite and apatite which indicate the magmatic origin. According to petrographic study, several processes have been found in green nephrite: Di→Dol, Tr→Di, Tr→Tr, Chl→Tr. The homogenization temperatures for the inclusions in tremolite in green nephrite range from 200 to 400°C. Test data of the stable isotopes of the ore forming fluid acquired at different temperatures show that the H and O isotopic values of green nephrite from the secondary deposit fall in the value range of existing marble type nephrite, but are remarkably different from values of other serpentine type nephrite deposits, as evidenced by a comparison with other types of nephrite deposits in the world. The results obtained by the authors show that green nephrite from secondary deposits was formed by contact metasomatism between magmatic rocks and marble, and that the ore forming fluid was derived from magmatic hydrothermal fluid and precipitation.

gems, spinel, inclusions

corundum, color.4, treatments.6, gems

There are some treatments for valuable color of blue sapphire such as dyeing, hea ng, di usion. Among of them, heat treatment with development of techniques and e ort has been performed for deriving beau ful blue color of sapphire un l nowadays. This tendency has been recognized that corundum is commonly undergone heat-treatment or enhancement. Improvement of the blue color of sapphire by hea ng started from the 19th century, it was started in earnest in the 20th century (Themelis, 1992). It needed oxidizing-reducing condi ons by gas di usion. The process modi es color of too dark or pale blue sapphire or removes unnecessary inclusions for clarity enhancement (Nassau, 1994). According to geographic origins of corundum, it has different characteristics such as color, impuri es, inclusions, etc. So, it needs to use a proper technique to change color. Therefore, it requires various condi ons and skills with experience of heat treatment to change color of sapphire. Some Koreans have a lot of interes ng in treatment techniques of gemstone for crea ng added value. A Korean company has developed a technique to enhance color of blue sapphire by applying with HPHT (high pressure and high temperature) apparatus. Originally, the apparatus was designed to grow synthe c diamond. It took many a empts with thousands of condi ons to nally get to valuable blue color from pale blue color, which is an unique process. The owner of the company explained that he had remade the HPHT apparatus and developed a mold for new treatment. It is no ceable news like Be-diffused corundum and HPHT treated diamond. The characteristic of new treated sapphire is found in infrared region. Earlier undetected, a strong absorption band at 3040-3050 cm-1 was observed after new treatment process. Therefore, infrared spectroscopy is effective in identifying the new treated sapphire, although we still unable to ascertain the absorp on band around 3040-3050 cm-1. We need to study to get more informa on of the newly treated sapphire by HPHT apparatus.

corundum, inclusions.5, gems

gems, garnet, asterism, exsolution, star garnet, phenomena

Regularly oriented orthopyroxene (opx) and forsterite (fo) inclusions occur as opx + rutile (rt) or fo + rt inclusion domains in garnet (grt) from Otrøy peridotite. Electron diffraction characterization shows that forsterite inclusions do not have any specific crystallographic orientation relationships (COR) with the garnet host. In contrast, orthopyroxene inclusions have two sets of COR, that is, COR-I: <111>grt//<001>opx and {110}grt∼//∼{100}opx (∼13° off) and COR-II: <111>grt//<011>opx and {110}grt∼//∼{100}opx (∼14° off), in four garnet grains analysed. Both variants of orthopyroxene have a blade-like habit with one pair of broad crystal faces parallel/sub-parallel to {110}grt plane and the long axis of the crystal, <001>opx for COR-I and <011>opx for COR-II, along <111>grt direction. Whereas the lack of specific COR between forsterite and garnet, along with the presence of abundant infiltrating trails/veinlets decorated by fo + rt at garnet edges, provide compelling evidence for the formation of forsterite inclusions in garnet through the sequential cleaving–infiltrating–precipitating–healing process at low temperatures, the origin of the epitaxial orthopyroxene inclusions in garnet is not so obvious. In this connection, the reported COR, the crystal habit and the crystal growth energetics of the exsolved orthopyroxene in relict majoritic garnet were reviewed/clarified. The exsolved orthopyroxene in a relict majoritic garnet follows COR-III: {112}grt//{100}opx and <111>grt//<001>opx. Based on the detailed trace analysis on published SEM images, these exsolved orthopyroxene inclusions are shown to have the crystal habit with one pair of broad crystal faces parallel to {112}grt//{100}opx and the long crystal axis along <111>grt//<001>opx. Such a crystal habit can be rationalized by the differences in oxygen sub-lattices of both structures and represents the energetically favoured crystal shape of orthopyroxene inclusions in garnet formed by solid-state exsolution mechanism. Considering the very different COR, crystal habit, as well as crystal growth direction, the orthopyroxene inclusions in garnet of the present sample most likely had been formed by mechanism(s) other than solid-state exsolution, regardless of their regularly oriented appearance in garnet and the COR specification between orthopyroxene and garnet. In fact, the crystallographic characteristics of orthopyroxene and the similar chemical compositions of garnet at opx + rt inclusion domains, fo + rt inclusion domains/trails and garnet rim suggest that the orthopyroxene inclusions in the garnet are most likely formed by similar cleaving–infiltration process as forsterite inclusions, though probably at an earlier stage of metamorphism. This work demonstrates that the oriented inclusions in host minerals, with or without specific COR, can arise from mechanism(s) other than solid-state exsolution. Caution is thus needed in the interpretation of such COR, so that an erroneous identification of exhumation from UHP depths would not be made.